Patent Publication Number: US-6211863-B1

Title: Method and software for enabling use of transcription system as a mouse

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-in-Part of U.S. Provisional Application No. 60/109,361, filed Nov. 20, 1998, U.S. Provisional Application No. 60/090,744, filed Jun. 26, 1998, and U.S. application Ser. No. 09/079,430, filed May 14, 1998, now U.S. Pat. No. 6,104,387 entitled Transcription System, all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a system for recording writing performed on a surface and its components and related methods where the position of a stylus used in the system to write on the surface is tracked using signals. 
     2. Description of Related Art 
     Existing technologies for capturing and storing handwritten notes include digitized writing surfaces such as electronic whiteboards or SMARTBOARDS™. These electronic whiteboards typically either photocopy an entire writing surface or serve as the actual input device (e.g. an electronic template) for capturing the handwritten data. The whiteboards may be active or passive electronic devices where the user writes on the surface with a special stylus. The active devices may be touch sensitive, or responsive to a light or laser pen wherein the whiteboard is the detector that detects the active signal. The passive electronic boards tend to use large, expensive, board-sized photocopying mechanisms. 
     As described above, whiteboard systems of the related art are large, cumbersome, expensive and immobile. 
     SUMMARY OF THE INVENTION 
     Various detectors for use in transcription systems according to the present invention are provided. In one embodiment, the detector comprises a signal receiver for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface, the signal receiver producing a timing signal in response to receiving the position signal; and a signal focussing element having a reflecting surface which is shaped and oriented relative to the signal receiver to reflect the position signal transmitted from the stylus onto the signal receiver. 
     In another embodiment, the detector comprises a signal receiver for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface, the signal receiver producing a timing signal in response to receiving the position signal; and a signal shielding element shaped and oriented relative to the signal receiver to reflect position signals transmitted by the stylus away from the signal receiver when the stylus is positioned outside a predetermined region of the writing surface. 
     In yet another embodiment, the detector comprises a signal receiver for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface, the signal receiver producing a timing signal in response to receiving the position signal; a signal focussing element having a reflecting surface which is oriented relative to the signal receiver to reflect the position signal transmitted from the stylus onto the signal receiver; and a signal shielding element shaped and oriented relative to the signal receiver to reflect position signals transmitted by the stylus away from the signal receiver when the stylus is positioned outside a predetermined region of the writing surface. 
     In regard to any of the detector embodiments, the signal shielding element is optionally shaped and oriented relative to the signal receiver to reflect position signals transmitted by the stylus away from the signal receiver when the stylus is positioned adjacent the writing surface outside of an angular range of about 70 to 110 degrees extending outward from the detector parallel to the writing surface, preferably about 90 degrees. The signal shielding element may also be optionally shaped and oriented relative to the signal receiver to reflect position signals transmitted by the stylus away from the signal receiver when the stylus is positioned adjacent the writing surface outside of an angular range of about 160 to 200 degrees extending outward from the detector parallel to the writing surface, preferably about 180 degrees. 
     In regard to any of the detector embodiments, at least a portion of the reflecting surface may have a curved shape such as a parabolic shape. The signal receiver may be positioned adjacent a focus of the parabolic shaped portion of the reflecting surface. 
     In regard to any of the detector embodiments, the detector may further comprise a mechanism for removably attaching the detector to the writing surface. 
     Other embodiments of detectors which may be used in the transcription system of the present invention, and variations thereof, are described herein and are intended to be encompassed within the scope of the present invention. 
     Various detector assemblies for use in transcription systems according to the present invention are also provided. In one embodiment, the detector assembly comprises first and second signal receivers for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface, the first and signal receivers each producing timing signals in response to receiving the position signal. 
     In another embodiment, the detector assembly comprises first and second signal receivers for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface, the first and signal receivers each producing timing signals in response to receiving the position signal; and a member coupling the first and second signal receivers, the coupling member being capable of adopting two or more configurations where a distance between the first and second signal receivers changes in at least two of the configurations. 
     According to this embodiment, the coupling member may be capable of telescopic expansion and contraction. The coupling member may also include a hinge by which the signal receivers can be angularly moved relative to each other. The coupling member may include at least two hinges. The coupling member may also include an attachment mechanism for removably attaching the detector assembly to a writing surface. The coupling member may optionally hold the first and second signal receivers a predetermined distance apart from each other when the detector assembly adopts at least one of the configurations. The coupling member may also include a locking mechanism for releasibly locking the detector assembly in at least one of the configurations. The locking assembly preferably holds the first and second signal receivers a predetermined distance apart from each other. The first and second signal receivers may be removably attachable to the coupling member. 
     Also according to this embodiment, the detector assembly may adopt a first configuration where the first and second signal receivers are separated from each other and a second configuration where the first and second signal receivers are positioned adjacent each other. The detector assembly may also adopt a first configuration where the first and second signal receivers are a first distance apart and a second configuration where the first and second signal receivers are a second distance apart that is less than 75% of the first distance, preferably less than about 50% of the first distance. The detector assembly may also be capable of adopting a first configuration having a first lateral footprint and second configuration having a second lateral footprint that is less than 75% of the first lateral footprint, preferably a second lateral footprint that is less than about 50% of the first lateral footprint. In one variation, the second lateral footprint that is between about 5% and 75% of the first lateral footprint. 
     In another embodiment, a detector assembly is provided which comprises a housing for mounting to the writing surface; a plurality of signal receivers; and at least one user activated control switch whose activation by a user when the detector assembly is mounted to the writing surface produces a control signal which causes the transcription system to perform a function in response. 
     According to this embodiment, activation of one of the control switches can cause an image displayed on a monitor operatively connected to the transcription system to be modified. Activation of one of the control switches can also cause at least a portion of an image displayed on a monitor operatively connected to the transcription system to be erased, saved, printed, electronically mailed, or facsimiled. Activation of one of the control switches can also cause a writing property associated with a stylus by the transcription system to be changed. Activation of one of the control switches can also cause a color associated with a stylus by the transcription system to be changed. 
     In regard to any of the detector assembly embodiments, the detector assembly may further comprise a mechanism for removably attaching the detector assembly to the writing surface. An example of such an attachment mechanism is a suction cup, preferably a cam activated suction cup. 
     In regard to any of the detector assembly embodiments, the detector assembly may further comprise a hardware unit which receives timing signals produced by the signal receivers, the hardware unit including logic for processing the timing signals to determine a time of flight of the position signal from the stylus to the signal receivers. 
     In regard to any of the detector assembly embodiments, the detector assembly may also further comprise a rectifier connected in series between the signal receivers and the hardware unit such that the hardware unit receives the timing signal from the signal receivers via the rectifier. 
     In regard to any of the detector assembly embodiments, the detector assembly may also further comprise a comparator connected in series between the rectifier and the hardware unit such that the hardware unit receives the timing signal from the rectifier via the comparator. 
     In regard to any of the detector assembly embodiments, the detector assembly may be designed to be operated under battery power. For example, the detector assembly may be operated under battery power from a laptop computer. The detector assembly may also be operated under battery power having a voltage between about 1.5 and 24 volts, preferably between about 1.5 and 12 volts. 
     In regard to any of the detector assembly embodiments, the detector assembly may further include a power source for operating the detector assembly. The power source may be a battery. The battery may have a voltage of between about 1.5 volts and 24 volts, preferably between about 1.5 volts and 12 volts. 
     In regard to any of the detector assembly embodiments, the detector assembly may optionally include any of the detector embodiments described above. In particular, the detector assembly may include signal focussing elements and/or signal shielding elements. 
     In regard to any of the detector assembly embodiments, the detector assembly may further include a microphone. The microphone may be used in the transcription system to record sound information during a transcription period and may be used to receive voice commands for operating the transcription system. 
     Other embodiments of detector assemblies which may be used in the transcription system of the present invention, and variations thereof, are described herein and are intended to be encompassed within the scope of the present invention. 
     Various styli for use in transcription systems according to the present invention are also provided. 
     In one embodiment, the stylus comprises a stylus housing defining a volume for housing a writing element and an opening on a distal end of the stylus housing through which a portion of the writing element extends for writing on a writing surface. 
     In another embodiment, the stylus comprises a stylus housing defining a volume for housing a writing element, an opening on a distal end of the stylus housing through which a portion of the writing element extends for writing on a writing surface, and a door on a side of the stylus housing which may be opened or removed and through which a writing element can be introduced into and removed from the stylus housing. 
     In another embodiment, the stylus comprises a stylus housing defining a volume for housing a writing element and an opening on a distal end of the stylus housing through which a portion of the writing element extends for writing on a writing surface, the stylus housing including a removable adapter for adjusting the volume of the housing to accommodate a particular type of writing element to be positioned within the housing. 
     According to this embodiment, the particular type of writing element may be selected from the group consisting of whiteboard marker, pen, pencil and chalk. The particular type of writing element may also be a color of writing element or a brand of writing element. The removable adaptor may be color coordinated with a color of the writing element. 
     In another embodiment, the stylus comprises a power level sensor for sensing the power level of a power source housed within the stylus; and a signal transmitter configured to transmit power signals having information concerning the power level of the power source. The stylus may further comprise logic coupled with the power level sensor for monitoring the power level and causing the power signal to be transmitted from the signal transmitter once the power level of the power source has fallen below a pre-determined level. The power level signal may be encoded into a position signal or a reference signal. The position signal may be a sonic signal. 
     In another embodiment, a stylus is provided which includes a position signal transmitter; and a stylus housing defining a volume for housing a removable writing element which includes a power source for providing operating power to the stylus, a portion of the volume for housing the writing element including a power source contact area for placing the stylus in electrical contact with the writing element power source. The stylus may optionally include a writing tip and a conduit for communicating writing media from the writing element to the writing tip. The stylus of this embodiment may optionally be part of a kit which includes a removable writing element including a writing element housing sized to fit within the volume of the stylus housing, writing media contained within the writing element housing, a power source for providing operating power to the stylus, and power source contacts positioned on the writing element housing such that the power source contact area is in electrical contact with the power source contacts when the writing element is positioned within the stylus housing. The present invention also relates to the writing element which includes the power source for providing operating power to the stylus. 
     Further according to this embodiment, the stylus and/or the writing element may include electronics which causes a signal to be transmitted by the stylus which identifies the stylus and/or the writing element as being compatible with the transcription system. In this regard, the stylus and/or the writing element may include logic for producing encoded identification signals, the transcription system also including logic for recognizing the encoded identification signals. By incorporating this feature, use of styluses and writing elements incompatible with the transcription system can be prevented by the system. 
     According to any of the stylus embodiments, the stylus may include a position signal transmitter for transmitting position signals, a reference signal transmitter for transmitting reference signals and/or a position signal receiver for receiving position signals. 
     According to any of the stylus embodiments, at least a portion of the stylus housing may be clear or opaque such that it is possible to see the writing element within the housing. The clear or opaque portion may be sized and positioned to allow a user to determine a color of the writing element through the portion. The clear or opaque portion may also be sized and positioned to allow a user to see an amount of writing media that the writing element contains. For example, when chalk, graphite or a liquid ink reservoir is used in conjunction with the writing element, it is also possible to observe how much writing media is remaining. 
     According to any of the stylus embodiments, the stylus housing may include an aperture which allows a user to rotate a writing element about its longitudinal axis housed within the stylus housing without having to disassemble the stylus housing or remove the writing element from the stylus housing. It is noted that some writing elements include a tip which is not symmetrical about the longitudinal axis of the writing element, such as a wedge shaped tip of a marker. In such instances, it may be desirable to periodically alter the angular positioning of the tip of the writing element. This may be accomplished by rotating the writing element through the aperture without having to remove the writing element from the stylus housing or having to disassemble the stylus. 
     According to any of the stylus embodiments, the stylus may further include a sensor adjacent the distal end of the stylus housing for detecting a condition of media in the stylus. For example, the stylus may include a sensor adjacent an end of the stylus housing out of which the writing element extends which serves to detect if the writing element is low on writing media. In one variation, the sensor detects a water content or another solvent content of the portion of the writing element extending from the housing, thereby alerting the user when the writing element needs to be replaced. 
     According to any of the stylus embodiments, the stylus may include a mechanism for distinguishing between different writing elements by only permitting a particular type of writing element (for example, based on color) to be positioned within the housing. In one variation, the writing element may have a shaped portion associated with a particular color, such as the end of the element opposing the tip. Meanwhile, the mechanism in the housing may have a shape which only allows a writing element having a particular shaped portion to fit within the housing, thereby preventing other types of writing elements from being positioned within the housing. This embodiment is useful for allowing a set of styluses to be color coded. 
     According to any of the stylus embodiments, the position signal transmitter may transmit a variety of signals including an ultrasound signal, a radar signal, or a micro-impulse radar signal. 
     According to any of the stylus embodiments, stylus may further include a reference signal transmitter for transmitting a reference signal when the writing element is sensed by the contact switch to be in contact with the writing surface. The reference signal transmitter may transmit a variety of signals including infra-red signals and ultrasound signals. 
     According to any of the stylus embodiments, the stylus may further include a contact switch for sensing when the writing element is contacted with a writing surface, the position signal transmitter transmitting the position signal when the writing element is sensed by the contact switch to be in contact with the writing surface. According to this variation, the stylus may further include a reference signal transmitter which transmits a reference signal when the writing element is sensed by the contact switch to be in contact with the writing surface. 
     According to any of the stylus embodiments, the stylus may further include a cap removably attachable to the stylus housing distal end and sized to cover the portion of the writing element which extends from the stylus housing distal end. The cap preferably forms a seal with the stylus housing to prevent the writing element from drying out. The cap may be formed of a material which allows a user to observe the color of the writing element without having to remove the cap. For example, the cap may optionally be clear or opaque. Also the position signal transmitter may be positioned adjacent the distal end of the stylus housing and the cap may be sized to fit over the position signal transmitter. 
     Other embodiments of styli which may be used in the transcription system of the present invention, and variations thereof, are described herein and are intended to be encompassed within the scope of the present invention. 
     The present invention also relates to the use of a temperature sensor for measuring a temperature adjacent the writing surface. The temperature sensor may be incorporated into one or more components of the transcription systems described herein, such as writing surfaces, styluses, detectors, detector assemblies, coupling members and sub-members, attachment members, hardware units, and templates. Changes in temperature can alter the speed at which position signals travel. Measurement of temperature using the temperature sensor can be used to account for these changes. 
     Various transcription systems embodiments can be designed in view of the present invention. Some specific examples of transcription systems embodiments are as follows. 
     In one embodiment, the transcription system includes a plurality of signal receivers for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface, the signal receivers producing timing signals in response to receiving the position signal from the stylus, the transcription system using the timing signals to determine a position of the stylus adjacent the writing surface. 
     In another embodiment, a transcription system includes at least one signal receiver for receiving a first power signal transmitted from a stylus and for producing a second power signal, the first and second power signal having information concerning a power level of a power source included in the stylus; a hardware unit receiving the second power signal from the at least one signal receiver and having logic for processing the second power signal to determine the power level of the power source; and an indicator coupled with the hardware unit to indicate to a user the power level of the power source within the stylus. 
     According to this embodiment, a signal receiver may be included in a detector which is configured to be coupled with the writing surface. Also according to this embodiment, the signal receiver may be included in a coupling member which couples a first detector to a second detector, the first and second detectors being in electrical communication with the hardware unit. According to this embodiment, the signal receiver may be included in the hardware unit Also according to this embodiment, the signal receiver may include a photo sensor and the power signal may be encoded into an infra-red signal transmitted from the stylus. Also according to this embodiment, the signal receiver may include a piezoelectric material and the power signal may be encoded in a sonic signal transmitted from the stylus. 
     Other embodiments of transcription systems according to the present invention are described herein and are intended to be encompassed within the scope of the present invention. 
     One or more components of the transcription systems described herein, such as detectors, detector assemblies, coupling members and sub-members, attachment members, hardware units, and templates can optionally be permanently incorporated into articles which can be used as writing surfaces, such as whiteboards, chalk boards, or furniture which includes either a writing surface or a mechanism for attaching a writing surface to the furniture. For example, it is envisioned that these components of the transcription system may be incorporated into desks and other types of office furniture. 
     Kits for use with the various embodiments of the transcription system and its components are also provided. In its broadest sense, kits are provided which include any two same or different components of the various embodiments of transcription systems described herein. Types of components provided herein include, but are not limited to writing elements, writing surfaces such as paper, whiteboards, chalkboards, and glass, styluses, stylus caps, detectors, detector assemblies, coupling members and sub-members, attachment members, hardware units, templates, and logic in computer readable form for use in the various transcription systems. 
     Some specific examples of kit embodiments are as follows. In one embodiment, a kit is provided which includes first and second signal receivers for positioning adjacent a writing surface and for receiving a position signal transmitted from a stylus when the stylus is positioned adjacent the writing surface. The signal receivers produce timing signals in response to receiving the position signal from the stylus. The kit also includes a template which is coupleable to the writing surface and which has markings defining a perimeter of at least one control section sized to have a writing portion of the stylus positioned within the perimeter of the at least one control section. The kit also includes a computer readable medium including logic for identifying when the portion of the stylus is positioned within the perimeter of a given control section and for directing a processing unit of the transcription system to carry out a function associated with the given control section. 
     In another embodiment, the kit includes a writing surface containing a background image. The kit also includes a computer readable medium including instructions which when performed by a processor to create the background image on a monitor. The computer readable medium also includes instructions for forming a composite image corresponding to a combination of the background image and the image written upon the writing surface. According to this embodiment, the writing surface may be a blank form, such as a spreadsheet. Using this kit, it is possible to take a blank form such as a spreadsheet and fill out the blank form on the writing surface while simultaneously recording the same blank form being filled out. 
     In yet another embodiment, a kit is provided for use with a transcription system which includes a plurality of signal receivers for positioning adjacent a writing surface and for receiving one or more position signals transmitted from a stylus when the stylus is positioned adjacent the writing surface, the signal receivers producing timing signals in response to receiving position signals from the stylus, the kit comprising: 
     a template coupleable to the writing surface, the template including one or more control sections; and 
     a computer readable medium including logic for detecting when the stylus contacts a particular control section based on receipt by the signal receivers of one or more position signals transmitted from the stylus and logic for causing a function to be performed by the transcription system in response to detecting that the stylus has contacted the particular control section. 
     According to this kit embodiment, the template may include a plurality of control sections, the logic for causing a function to be performed including logic for causing different functions to be performed depending on which of the plurality of control sections are contacted by the stylus. 
     According to this kit embodiment, the template may be comprised of a sheet of paper or plastic. The template may be devoid of electronic circuitry. The template may also not send or receive signals. 
     Also according to this kit embodiment, the template may include at least two calibration marks and the computer readable medium includes logic for determining a position of the template on the writing surface relative to the signal receivers based on the stylus contacting the template at the at least two calibration marks. 
     According to this kit embodiment, the computer readable medium may include logic for causing an image displayed on a monitor operatively connected to the transcription system to change when the stylus contacts a particular control section. 
     According to this kit embodiment, the computer readable medium may include logic for causing an image displayed on a monitor operatively connected to the transcription system to be saved when the stylus contacts a particular control section, deleted when the stylus contacts a particular control section, printed when the stylus contacts a particular control section, facsimiled when the stylus contacts a particular control section, or electronically mailed when the stylus contacts a particular control section. 
     According to this kit embodiment, the one or more control sections may include control sections for performing calculator functions, the computer readable medium including logic for performing the calculator functions when the stylus contacts particular control sections. 
     According to this kit embodiment, the computer readable medium may include a data file identifying the positions of the control sections of the template. 
     According to this kit embodiment, the kit may include a plurality of different templates and the computer readable medium may include one or more data files for the plurality of different templates which identify positions of control sections on each template, the computer readable medium further including logic which allows a user to select which of the plurality of templates is going to be used. 
     According to this kit embodiment, the computer readable medium may include logic which allows a user to specify what function is performed by the transcription system in response to the stylus contacting a particular control section. 
     In another embodiment, a kit is provided for use with a transcription system which includes a plurality of signal receivers for positioning adjacent a writing surface and for receiving position signals transmitted from a stylus when the stylus is positioned adjacent the writing surface, the transcription system recording writing performed by the stylus on the writing surface. According to this embodiment, the kit comprises 
     a background image coupleable to the writing surface; and 
     a computer readable medium including 
     logic for detecting a position of the background image on the writing surface, 
     logic for detecting a position of the stylus relative to the background image on the writing surface, 
     logic for recording writing by the stylus relative to the background image, and 
     logic for forming a composite image comprising the background image and the writing by the stylus on the background image. 
     According to this embodiment, the background image may comprise a sheet of paper or plastic. The background image may be formed of a material which allows the writing by the stylus to be erased. The background image may be devoid of electronic circuitry and does not send or receive signals. The background image may comprises a blank form of a computer application or a spreadsheet. The background image may comprise at least two calibration marks and the computer readable medium includes logic for determining a position of the background image on a writing surface based on the stylus being positioned adjacent to the background image at the at least two calibration marks. 
     The computer readable medium may optionally include logic for causing an image displayed on a monitor operatively connected to the transcription system to change when the stylus is placed adjacent to a particular portion of the background image. 
     The computer readable medium may optionally include logic for causing the composite image to be saved, deleted, printed, facsimiled, or electronically mailed when the stylus is placed adjacent to a particular portion of the background image. 
     Although various versions of computer readable medium are described above as being a part of various kit embodiments, it is noted that the computer readable medium may also be provided separately from the kits. 
     A variety of different methods are also provided for use with transcription systems according to the present invention. 
     In one embodiment, a method is provided which comprises: 
     positioning a pad adjacent the writing surface, the pad including one or more input sections; 
     positioning the stylus adjacent a particular input section, the stylus transmitting a position signal in response; 
     having the transcription system determine that the stylus has been positioned adjacent the particular input section and perform a function associated with the particular input section in response. 
     According to this embodiment, the input section may be a calibration mark, the function performed by the transcription system being calibration of the transcription system by determining a separation between the signal receivers. 
     Also according to this embodiment, the function associated with the input section may be modifying an image displayed on a monitor operatively connected to the transcription system, the transcription system modifying the image in response to determining that the stylus contacted the save input section. The function associated with the input section may also be saving an image displayed on a monitor operatively connected to the transcription system, the transcription system saving the image in response to determining that the stylus contacted the save input section. The function associated with the input section may also be erasing an image displayed on a monitor operatively connected to the transcription system, the transcription system erasing the image in response to determining that the stylus contacted the save input section. The function associated with the input section also may be changing a color of an image displayed on a monitor operatively connected to the transcription system, the transcription system changing the color of the image in response to determining that the stylus contacted the save input section. 
     Associated with this method is a computer readable medium including: 
     logic for taking a file encoding positions of one or more input sections on a pad to be positioned adjacent the writing surface and associating with the one or more input sections a function to be performed when the stylus is detected as having been positioned adjacent to one of the input sections; 
     logic for determining that the stylus has been positioned adjacent to a particular input section based on times of flight of position signals from the stylus adjacent the particular input section to the plurality of signal receivers; and 
     logic for causing the transcription system to perform the function associated with the input section in response to determining that the stylus has been positioned adjacent to the particular input section. 
     In one variation, the function associated with the input section may be modifying an image displayed on a monitor operatively connected to the transcription system, the logic for causing the transcription system to perform a function including logic for causing the transcription system to modify the image in response to determining that the stylus contacted the save input section. 
     In another variation, the function associated with the input section is saving an image displayed on a monitor operatively connected to the transcription system, the logic for causing the transcription system to perform a function including logic for causing the transcription system to save the image in response to determining that the stylus contacted the save input section. 
     In yet another variation, the function associated with the input section is erasing an image displayed on a monitor operatively connected to the transcription system, the logic for causing the transcription system to perform a function including logic for causing the transcription system to erase the image in response to determining that the stylus contacted the save input section. 
     Also associated with this method is a transcription system comprising: 
     a stylus which transmits position signals when positioned adjacent a writing surface; 
     a plurality of signal receivers for positioning adjacent the writing surface which receive the position signals transmitted from the stylus and produce timing signals in response; 
     a pad for positioning adjacent the writing surface, the pad including one or more input sections; and 
     a processing unit including logic for taking a file encoding positions of the one or more input sections on the pad and associating with each input section a function to be performed when the stylus is detected as having been positioned adjacent the input section, logic for determining that the stylus has been positioned adjacent an input section based on times of flight of position signals from the stylus adjacent the input section to the plurality of signal receivers, and logic for causing the transcription system to perform the function associated with the input section in response to determining that the stylus has been positioned adjacent to the input section. According to this embodiment, the function may be selected from the group consisting of modifying, saving, and erasing an image displayed on a monitor operatively connected to the transcription system. Also according to this embodiment, the input section may be a calibration mark and the function performed by the transcription system is calibration of the transcription system by determining a separation between the signal receivers. 
     A method is also provided comprising: 
     activating a user activated control switch mounted on the writing surface; 
     producing as a result of activating the user activated control switch a control signal which is communicated to the transcription system; and 
     having the transcription system perform a function in response to receiving the control signal. 
     According to the method, activation of the control switch may cause at least a portion of an image displayed on a monitor operatively connected to the transcription system to be modified. 
     Also according to the method, activation of the control switch may cause at least a portion of an image displayed on a monitor operatively connected to the transcription system to be erased, saved, printed, electronically mailed or facsimiled. 
     In another embodiment, a method is provided which comprises positioning a background image adjacent the writing surface such that the background image can be seen by a user; 
     having the transcription system determine a position of the background image relative to the signal receivers; 
     having the user write adjacent the background image using the stylus such that the user sees a composite image comprising the background image and the writing; 
     having the transcription system detect the writing by detecting the position of the stylus; and 
     having the transcription system create an electronic equivalent of the composite image by combining the background image with the writing. 
     According to the method, the method may further comprise displaying the electronic equivalent of the composite image on a monitor operatively connected to the transcription system. 
     Also according to the method, positioning the background image adjacent the writing surface may include attaching a sheet of material including the background image adjacent the writing surface. 
     Also according to the method, the sheet may be attached to the writing surface. The sheet may be erasable. The sheet may comprise paper or plastic. 
     Also according to the method, the writing surface may be translucent and the sheet may be positioned behind the writing surface. 
     Also according to the method, positioning the background image adjacent the writing surface may include displaying the background image adjacent the writing surface. Displaying the background image adjacent the writing surface can include projecting the background image onto the writing surface. 
     Also according to the method, the background image may comprise a screen from a computer application. The background image may comprise a variety of images including a website, a spreadsheet, or a grid. 
     According to the method, the background image may comprise at least two calibration marks and determining a position of the background image relative to the signal receivers may include placing the stylus adjacent the calibration marks. 
     Also according to the method, the background image may comprise one or more control sections, the method further including causing the transcription system to perform a function by placing the stylus adjacent one of the control sections. The function performed by the transcription system may include modifying an image displayed on a monitor operatively connected to the transcription system. The function performed by the transcription system may also include removing at least a portion of the composite image from an image displayed on a monitor operatively connected to the transcription system, saving the electronic equivalent of the composite image, deleting the electronic equivalent of the composite image, and printing the electronic equivalent of the composite image. 
     In another embodiment, a method is providing for correcting for the effect of temperature on the speed of ultrasound signals in the transcription system. The method comprises measuring a temperature adjacent a writing surface where an ultrasound transcription system is being employed; and adjusting time of flight calculations using the measured temperature adjacent the writing surface. Temperature is preferably measured periodically in order to account for changes in condition, for example, a change in whether sunlight is impacting upon the writing surface. This method may be employed in combination with any of the other methods of the present invention, According to these methods, temperature sensors may optionally be incorporated into the stylus, template and/or positioned adjacent one or more of the detectors. 
     A method is also provided for forming or modifying an image displayed on a monitor or projected on a surface by forming that image or modifying that image on a writing surface using a stylus and transcription system of the present invention. It is noted that modifying the image may include erasing a portion of the image on the writing surface which causes the erased portion to be removed from the monitor or projected image. 
     A variety of calibration methods are provided. In one embodiment, the calibration method comprises: 
     attaching the plurality of signal receivers to the writing surface at unknown distances from one another, each signal receiver including a calibration mark at a known position relative to the signal receiver; 
     transmitting position signals from each calibration mark; and 
     using times of flight of the position signals to determine separation distances between the plurality of signal receivers. 
     According to this embodiment, the position signals may be transmitted from a stylus by contacting the stylus to the calibration marks. 
     In another embodiment, a method is provided which comprises: 
     positioning a pad adjacent the writing surface, the pad including a plurality of calibration marks; 
     positioning the stylus adjacent to each calibration mark, the stylus transmitting a position signal to the signal receivers in response; 
     having the transcription system determine separations between the signal receivers based on times of flight between the calibration mark and the signal receivers. 
     According to this embodiment, two calibration marks and two signal receivers may be utilized to perform the method. 
     In another embodiment, the method comprises: 
     attaching a template to the writing surface, the template having two or more calibration marks at known separation distances from one another; 
     transmitting position signals from a stylus at the two or more calibration marks to at the signal receivers; 
     using times of flight of the position signals from the calibration marks to the signal receivers to determine separation distances between the calibration marks and the signal receivers; and 
     using the determined separation distances between the calibration marks and the signal receivers and the known separation distances between the calibration marks to determine separation distances between the signal receivers. 
     According to this embodiment, the method may optionally further include determining the position of the template on the writing surface relative to the signal receivers. Also according to this embodiment, the template may include one or more control sections at known positions relative to the calibration marks, the method further including determining the position of the one or more control sections relative to the signal receivers. 
     Associated with these calibration methods are computer readable medium for performing all or a portion of these methods. 
     In one embodiment, the computer readable medium comprises: 
     logic for taking times of flight of position signals from calibration marks on a template attached to a writing surface to a plurality of signal receivers attached to the writing surface, the calibration marks being at known separation distances from each other, and using the times of flight to determine separation distances between the calibration marks and the signal receivers; and 
     logic for using the determined separation distances between the calibration marks and the signal receivers and the known separation distances between the calibration marks to determine separation distances between the signal receivers. 
     According to this embodiment, the computer readable medium may further include logic for determining the position of the template on the writing surface relative to the signal receivers. 
     Also according to this embodiment, the template may include one or more control sections at known positions relative to the calibration marks, the computer readable medium further including logic for determining the position of the one or more control sections relative to the signal receivers. 
     Also according to this embodiment, the template may include a mouse region which serves as a virtual touch pad for the user. In this regard, the user can move the stylus within the mouse region and cause a cursor associated with the system to move. Thus, by moving the stylus within the mouse region, the stylus can serve as a mouse for the system. In this embodiment, the system includes logic for utilizing the movement of the stylus within the system as a mouse. 
     Also according to this embodiment, the template may include a graffiti region which can recognize handwritten signals, such as handwriting graffiti used with the PALM PILOT. In this embodiment, the system includes logic for utilizing the movement of the stylus within the graffiti region and translating that movement into handwritten signals. 
     In another embodiment, the computer readable medium includes logic for taking times of flight of position signals from calibration marks to signal receivers and using the times of flight to determine separation distances between the signal receivers. 
     It is noted in regard to methods of the present invention that these methods employ logic and a processor for executing the logic. The logic may be software or firmware and may be stored in any form of computer-readable medium including diskettes, CDs, and hard drives. The logic may also be maintained on a server. The present invention is intended to encompass any device which includes logic for performing any method according to the present invention. The present invention is also intended to encompass any form of computer-readable medium which includes logic for performing any method according to the present invention. 
     Each of the above methods is preferably performed by a processor. Accordingly, an aspect of the present invention relates to a computer-readable medium, such as a diskette, CD, or hard drive which including instructions to be carried out by a processor for performing the various methods of the present invention. The present invention also relates to a computer, PDA, server, and the like which incorporates logic for performing the various methods of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1A illustrates several components of a transcription system. 
     FIG. 1B illustrates installation of the transcription system. 
     FIG. 1C illustrates calibration of a transcription system. 
     FIG. 1D illustrates operation of a transcription system. 
     FIG. 1E illustrates operation of an eraser which can be used with a transcription system. 
     FIG. 1F illustrates operation of a template having control sections corresponding to the key pad of a calculator. 
     FIG. 1G illustrates a template with control sections and icons indicating the function correlated with each control section. 
     FIG. 1H illustrates a stylus creating a written image on a writing surface containing a background image to form a composite image while the same composite image is being formed on the monitor. 
     FIG. 1I illustrates a composite image comprising an image of a webpage projected onto a writing surface and writing on the writing surface in combination to with the composite image being displayed on a monitor and projected on a separate surface. 
     FIGS. 2A illustrates a transcription system where a stylus receives a reference signal and transmits a position signal. 
     FIG. 2B illustrates a transcription system where a stylus receives a reference signal via an electrical wire. 
     FIG. 2C illustrates a transcription system where a stylus transmits a position signal and a reference signal. 
     FIG. 2D illustrates a transcription system where a stylus transmits two different reference signals in response to receiving different position signals. 
     FIG. 3A illustrates dimensions of a writing area. 
     FIG. 3B illustrates a transcription system where a first detector includes a position signal transceiver or transmitter for responding to a reference signal from a second detector. 
     FIG. 3C illustrates a transcription system where a first detector includes a calibration mark for calibrating the transcription system. 
     FIG. 3D illustrates a detector assembly where a first and second detectors are separated by a coupling member. 
     FIG. 3E illustrates a detector assembly where a first and second detectors are positioned along a side of the writing area. 
     FIG. 4A is a side view of a stylus which may be used in a transcription system according to the present invention. 
     FIG. 4B is a side view of a stylus including a removable cap. 
     FIG. 4C is a disassembled side view of a stylus including a stylus housing, a door and a stylus. 
     FIG. 4D is a side view of the stylus illustrated in FIG. 4C assembled. 
     FIG. 4E is a side view of a stylus coupled to a transcription system by an electrical wire for providing a reference signal to the stylus. 
     FIG. 4F is a side view of a cap according to the present invention. 
     FIG. 4G is a side view of a stylus with a cap in place. 
     FIG. 4H is a cross section of a stylus coupled with a cap adapted to accommodate a position signal transmitter or receiver. 
     FIG. 4I is a cross section of a stylus coupled with a cap adapted to accommodate a position signal transmitter or receiver. 
     FIG. 4J is a cross section of a stylus with a ridge coupled with a cap a cap adapted to accommodate a position signal transmitter or receiver. 
     FIG. 4K illustrates a stylus embodiment where the stylus electronics are positioned toward a distal end of the stylus adjacent the tip. 
     FIG. 4L illustrates a stylus embodiment where an elongated writing element is employed which allows the diameter of the stylus to be further reduced. 
     FIG. 5A is a side view of an eraser for use with a transcription system. 
     FIG. 5B is a bottom view of the eraser illustrated in FIG.  5 A. 
     FIG. 6A is a side view of a detector. 
     FIG. 6B is a bottom view of a detector. 
     FIG. 7A is a perspective view of a detector including a 180 degree range of reception. 
     FIG. 7B is a side view of a detector including a 180 degree range of reception. 
     FIG. 7C is a perspective view of a detector including a 90 degree range of reception. 
     FIG. 7D illustrates a detector assembly which includes a hardware unit with control switches and indicators. 
     FIG. 7E is a side view of a detector assembly with a coupling member which serves as a hardware unit. 
     FIG. 7F is a top view of a detector assembly with a coupling member which serves as a hardware unit. 
     FIG. 7G is a top view of a detector assembly capable of adopting two or more configurations. 
     FIG. 7H is a side view of a detector assembly capable of adopting two or more configurations. 
     FIG. 7I is a side view of a detector assembly having first and second hinges which permit the detector assembly to adopt two or more configurations. 
     FIG. 7J is a side view of a detector assembly where a coupling member is constructed from a second member slidably positioned within a first member. 
     FIG. 7K is a top view of a detector assembly where a coupling member is constructed from a second member is slidably positioned within a first member. 
     FIG. 7L is a side view of a detector assembly where a coupling member is constructed from first and second members which are detachable from one another. 
     FIG. 7M illustrates a user activatable attachment mechanism which can be used to coupled a detector or coupling member with a writing surface. 
     FIG. 7N illustrates a detector with a shielding element which shields a position signal receiver from position signals transmitted from outside a predetermined region extending over about 90 degrees. 
     FIG. 7O illustrates a detector with a shielding element which shields a position signal receiver from position signals transmitted from outside a predetermined region extending over about 180 degrees. 
     FIG. 8A illustrates a block diagram which can be used with the system illustrated in FIG.  2 A. 
     FIG. 8B illustrates a block diagram which can be used with the system illustrated in FIG.  2 C. 
     FIG. 8C illustrates a block diagram which can be used with the system illustrated in FIG.  2 D. 
     FIG. 9 is a circuit for triggering transmission of a position signal in response to receiving a reference signal. 
     FIG. 10 is a circuit which can be used to detect when a position signal has been received at a detector. 
     FIG. 11A illustrates dimensions of writing area and monitor image area. 
     FIG. 11B illustrates coordinate systems transposed on the writing area and the monitor image area when the first and second detectors are position along the top of the writing area. 
     FIG. 11C illustrates coordinate systems transposed on the writing area and the monitor image area when the first and second detectors are position along a side of the writing area. 
     FIG. 11D illustrates creation of a monitor image. 
     FIG. 12 is a block diagram of a processing unit. 
     FIG. 13 illustrates an image data structure used to store a series of stylus positions. 
     FIG. 14 is a implement characteristic data structure used to identify whether an implement is an eraser or a stylus and to identify the characteristics of each stylus. 
     FIG. 15A is an control section relative to template data structure. 
     FIG. 15B is an control section relative to detectors data structure. 
     FIG. 16A is a process flow of a calibration module. 
     FIG. 16B is a process flow for determining the dimensions of a writing area in a transcription system as illustrated in FIG.  3 B. 
     FIG. 17 is a process flow for determining the positions of the stylus relative to the detectors and creating the monitor image from the determined positions. 
     FIG. 18 is a process flow for erasing a monitor image by erasing the written image. 
     FIG. 19A is a process flow for stylus identification logic. 
     FIG. 19B is a process flow for stylus identification logic which is complementary to the process flow illustrated in FIG.  19 A. 
     FIG. 20 illustrates background image calibration logic. 
     FIG. 21 illustrates an embodiment of a transcription system kit. 
     FIG. 22 illustrates a stylus which has been taken apart so that a marker can be placed within the stylus. 
     FIG. 23A illustrates a side view of the stylus where the stylus cover is in full view. 
     FIG. 23B illustrates a side view of the stylus where the stylus cover is on top and the stylus body is below. 
     FIG. 24A illustrates the detector assembly unfolded. 
     FIG. 24B illustrates the detector assembly attached to a whiteboard surface via the suction cup assemblies. 
     FIG. 24C illustrates the user inputs on the detector assembly. 
     FIG. 25 illustrates how the detector assembly can be attached to a processor via a connection cable. 
     FIG. 26A illustrates a user interface for the transcription system. 
     FIG. 26B illustrates a whiteboard with a detector assembly attached and a smiley face written using a transcription system stylus. 
     FIG. 26B also illustrates the user interface which shows an electronically transcribed image of the smiley face. 
     FIG. 27A illustrates the user interface in greater detail and some of the functions which the user interface  550  performs. 
     FIG. 27B illustrates the display toolbar and its operation. 
     FIG. 27C illustrates the navigation toolbar and its operation. 
     FIG. 27D illustrates the template in greater detail. 
     FIG.  27 E( 1 ) illustrates the template and the detector assembly on a writing surface. 
     FIG.  27 E( 2 - 4 ) illustrate a sequence of images displayed on a user interface to allow the transcription to determine the position of the template relative to the detector assembly on the writing surface 
     FIG. 28A illustrates a window which allows the user to configure the writing surface. 
     FIG. 28B illustrates a window which allows the user to configure the stylus. 
    
    
     DETAILED DESCRIPTION 
     Transcription System Overview 
     The present invention relates to a system for recording writing performed on a surface and its components and related methods where the position of a stylus used in the system to write on the surface is tracked using signals. Writing is intended to include the formation or modification of any type of image on a surface by a writing element, including printing, drawing, sketching, erasing and the like. The surface on which the writing is performed may be any surface on which writing may be performed. Examples of suitable surfaces include but are not limited to, whiteboards, blackboards, clipboards, desktops, walls, projection screens, flip chart tablets, and glass panes whether or not covered by a material such as paper, glass, metal, or plastic which can be written upon. The surface is preferably a relatively smooth and relatively flat surface, although it is noted that the surface may have a degree of curvature. 
     In a system according to the present invention, a stylus including a housing and a writing element is provided. The writing element may optionally be removable from the housing. In one embodiment, the writing element is removed from an end of the housing while in another embodiment the writing element is removable from a side of the stylus housing. Also provided are two or more detectors which may be permanently or removably affixed to a writing surface and are used in combination with the stylus to detect the position of the stylus on the writing surface. Also provided in the system is hardware for controlling when reference and position signals, described herein, are sent between the stylus and the two or more detectors. 
     The system may also include a processing unit which contains logic and processing capabilities for performing the various calibration and calculation functions necessary to determine the position of the stylus relative to the two or more detectors at multiple times over a period of time that the stylus is used to write. Alternatively, the system may produce signals corresponding to timing data which can be communicated to a processor external to the system for providing positioning data. 
     Incorporated into the stylus and the plurality of detectors are one or more transmitters and one or more receivers for transmitting and receiving signals between the stylus and detectors. Used in combination, the one or more transmitters and one or more receivers determine a separation between the stylus and the plurality of detectors based on a time of flight of the signals between them which can be used to determine a positioning of the stylus. As will be discussed in greater detail below, a variety of ranging media can be used in the system including, for example, ultrasound and radar, such as MIR. 
     FIG. 1A illustrates one embodiment of a transcription system according to the present invention. As illustrated, the system includes a stylus  10 , a first detector  12 A, a second detector  12 B and a hardware unit  14 . As illustrated, the system can optionally include an eraser  16 , template  18 , processing unit  20 , monitor  22  and user interface  24 . The user interface can be typical devices which allow users to interact with processing unit, hardware controllers and other processor based systems. For instance, the user interface can include a keyboard, and/or a mouse or even a touchpad imposed on the monitor  22 . 
     Signals from the first detector  12 A and the second detector  12 B may be transmitted to the hardware unit  14  through a wire  26 . These signals may be electrical or optical in nature. The signals can also be transmitted wirelessly to the hardware unit  14 , for example through a form of electromagnetic radiation. As will be explained below, the system can also be designed such that signals are transmitted from the stylus  10  or the eraser  16  to the hardware unit  14 . Suitable wires for transmitting the signals include cables similar to the cables used for standard telephone to jack connections. The detectors  12 A,  12 B and the hardware unit  14  can include ports which receive the cables which can be easily withdrawn from the ports. 
     FIG. 1B illustrates how the transcription system illustrated in FIG. 1A may be installed relative to a writing surface  28 . The first detector  12 A and the second detector  12 B are removably coupled to the writing surface  28 . As illustrated by the arrows  30 , the first detector  12 A and second detector  12 B can be placed anywhere on the writing surface  28 . However, it is generally preferred that the first detector  12 A and the second detector  12 B be positioned adjacent an edge of the writing surface  28 . It is also noted that the first detector  12 A and the second detector  12 B may optionally be permanently attached to the writing surface  28 . 
     As illustrated in FIGS. 1A and 1B, a template  18  positioned on or adjacent to the writing surface can be used to control the transcription system using a stylus adjacent the writing surface. As illustrated, the template  18  includes markings which define the perimeter of several control sections  32 . The control sections on the template  18  can be used to initiate functions which are carried out by the hardware unit  14  and/or the processing unit  20 . An advantage of the template is that it allows the user to control the monitor image  34  and the transcription system through the template as opposed to the user interface  24 . 
     Examples of functions that can be associated with a control section include, but are not limited to, causing the current monitor image  34  to be saved; causing the current monitor image  34  to be saved and moved to the background while a new monitor image area  36  is brought to the foreground for the creation of a new monitor image  34 ; causing the current monitor image  34  to be moved to the background while a new monitor image area  36  is brought to the foreground for the creation of a new monitor image  34 ; causing a copy of the current monitor image to be saved in the background while the current monitor image remains in the foreground for any additional adjustments; causing the entire monitor image  34  to be erased while retaining the current monitor image area  36  in the foreground; bringing a new monitor image area  36  into the foreground; maximizing the size of the current monitor image area  36  to fill the available space on the monitor; bringing the last monitor image area  36  to the foreground when another program was last used in the foreground; initiating calibration or recalibration of the transcription system; enabling or disabling selected functions; changing or selecting the color of particular strokes on the monitor image  34  or changing the particular color correlated with a particular stylus  10 ; faxing the monitor image  34 ; E-mailing the monitor image  34 ; and/or printing the monitor image  34 . 
     In one embodiment, the template includes a mouse region which serves as a virtual touch pad for the user. In this regard, the user can move the stylus within the mouse region and cause a cursor associated with the system to move. Thus, by moving the stylus within the mouse region, the stylus can serve as a mouse for the system. In this embodiment, the system includes logic for utilizing the movement of the stylus within the system as a mouse. 
     In another embodiment, the template includes a graffiti region which can recognize handwritten signals, such as handwriting graffiti used with the PALM PILOT. In this embodiment, the system includes logic for utilizing the movement of the stylus within the graffiti system and translating that movement into handwritten signals. 
     A background image can also be positioned on the writing surface. Alternatively, the background image may be projected onto or printed onto the writing surface itself. In a sense, the background image serves as a template for forming a composite image comprising a combination of the written image and the background image. One or more control sections can be used in combination with the background image in order to align the positioning of the written image relative to the background image so that the composite image recorded by the system is substantially the same as the composite image formed on the writing surface by the user. 
     The background image may include a blank form of a computer application, such as an EXCEL spreadsheet or a POWERPOINT slide. As a result, writing within the blank form causes entries to be entered into the corresponding locations in the computer program as they appear on the background image. The background image can also be graphics, such as a webpage, where the user writes on the writing surface and thereby edits the graphics by forming a composite image. 
     The control sections  32  can also be used to control the various functions of other programs. For instance, during a presentation to a group, the transcription system can be used simultaneously with other programs such as POWER POINT. For example, positioning the writing portion of the stylus within a particular control section  32  can cause POWER POINT to move to the next slide or display. Similarly, positioning the writing portion of the stylus within a different section  32  can cause POWER POINT to move to the previous slide or display. As a result, a user can scroll through the slides of a presentation and capture any notes the user makes on a writing surface  28  during the presentation. In this regard, the template can also function as a remote control or mouse for the system for various computer applications. 
     As can be seen from the above illustrative list of how a template can be used, a wide variety of additional system functions can be envisioned and are intended to fall within the scope of the present invention. The various control sections of the template can be defined with different colored sections of the template  18  or outlined sections of the template  18 . 
     Templates used with the system can be selected from a series of different templates stored into memory which are recognized by the transcription system. In use, the system is instructed as to which template has been selected. Optionally, the template may be selected by printing the template out from memory. Once selected, the template is placed adjacent the writing surface. 
     Templates may also be user defined. In one variation, a template is user defined within a program employed with the system. The user defined template is then printed out and the system is instructed that template will be used. In another variation, a template is user defined by drawing the template on the writing surface in combination with instructing a program employed with the system that the template being drawn is to be used. Predetermined control signal images, in combination with handwriting recognition can be used to assist the system in reading the template into memory that is drawn on the writing surface. 
     The template  18  can be constructed from any material suitable for attaching to a flat surface such as a piece of paper on which a template has been printed and a thin plastic sheet which can attach itself to the writing surface  28  via static cling. A feature of the present invention is that the template may be devoid of electronic circuitry and need not receive or transmit any signals. 
     When a template is employed, the template is preferably positioned at a distance from the first detector and the second detector. For example, in FIG. 1A the template  18  is illustrated as being positioned on an opposite side of a writing area  38  relative to the first detector  12 A and the second detector  12 B. Where possible, the template  18  is more preferably positioned approximately equidistant from each of the first detector  12 A and the second detector  12 B on the opposite side of the writing area  38  from the first detector  12 A and the second detector  12 B. Although the template  18  is shown to be removably attachable to the writing surface  28 , it is noted that the template  18  may optionally be permanently attached to the writing surface  28 . 
     In one embodiment, the transcription system is readily attachable to and detachable from different writing surfaces  28 . Detachability enables the transcription system to be portable and to be used with different writing surfaces  28  and with different sized writing surfaces  28 . It is noted that attachment to a writing surface is intended to encompass attachment adjacent to a writing surface. 
     As will be explained below, when the transcription system is used with different writing surfaces  28 , it may be necessary to calibrate the system. During calibration, the distance between the detectors, L, can be determined. In some embodiments of the system, the dimensions of the writing area  38  are determined including the writing area width, W; the writing area height, H; and the diagonal distance of the writing area, D. In other embodiments, the position of the template  18  is determined during the calibration. 
     Some embodiments of the system are self-calibrating, for example when the distance between detectors is fixed. In other embodiments, the system needs to be calibrated by the user. A variety of different calibration methods have been developed which optionally include entering information into the user interface  24  and/or by the user following a series of computer prompts. 
     FIG. 1C illustrates an example of a system which is calibrated by the user following a series of computer prompts. As illustrated, during the calibration, the user contacts one or more different calibration marks  40  on the template  18  with the stylus  10 . The calibration marks  40  can be positioned on the template  18  as illustrated. The calibration marks  40  can also be positioned on one or both the detectors  12 A,  12 B. 
     To prompt the user, the processing unit  20  may optionally produce an image on the monitor  22 . For instance, the processing unit  20  can create a template image  42  on the monitor  22  as illustrated in FIG.  1 C. An image of a stylus can be shown contacting a calibration mark  40  of the template image  42 . In response, the user contacts the stylus  10  with the calibration mark  40  on the template  18  as illustrated. In another embodiment, the processing unit  20  can create an image of a stylus contacting a calibration mark  40  on an image of a detector. In response, the user contacts a calibration mark  40  on the first detector  12 A. The transcription system will be calibrated after the user follows each prompt provided by the processing unit  20 . Because the transcription system is easily calibrated by the user, the transcription system is readily usable with different sized writing surfaces  28 . 
     After the transcription system has been calibrated, the system is generally ready for use. As illustrated in FIG. 1D, the user can write in the writing area  38  with the stylus  10 . While the user is creating an image in the writing area  38 , a similar image appears in a monitor image area  36  of the monitor  22 . The image in the writing area  38  is referred to as the written image  44  and the image on the monitor  22  is referred to as the monitor image  34 . As illustrated in FIG. 1E, the written image  44  can also be erased using an eraser  16 . The monitor image  34  is erased as the written image  44  is erased using the eraser  16 . 
     Optionally, the system is periodically recalibrated during operation to account for temperature changes adjacent the writing surface. Changes in temperature can occur, for example, due to a change in whether sunlight is impacting upon the writing surface (e.g., opening or closing blinds, passage of time). These temperature changes can alter the speed at which position signals travel. Measurement of temperature can be used to detect these temperature changes and recalibrate the system accordingly. In one variation, a method is providing for correcting for the effect of temperature on the speed of ultrasound signals in the transcription system comprising measuring a temperature adjacent a writing surface where an ultrasound transcription system is being employed; and adjusting time of flight calculations using the measured temperature adjacent the writing surface. This method may be employed in combination with any other calibration method. 
     The monitor image  34  can be stored for later editing and manipulation or can be converted to a number of electronic and digital document formats including, but not limited to, fax, e-mail, word processing programs such as WORD and WORDPERFECT, graphic presentation and preparation programs such as POWERPOINT, VISIO and design programs such as AUTOCAD. The monitor image can also be communicated in real time to remote users via a network, the INTERNET, phone lines or other communication media. The monitor image can also be projected either where the written image is being formed or in a remote location. In one embodiment, sound present in the location where the written image is being formed and modified is stored and/or communicated in combination with the monitor image. 
     FIG. 1F illustrates one embodiment of a template  18  which includes control sections  32  which correlate to the keys on a calculator keypad. The template  18  includes a plurality of control sections  32  corresponding to the keys on a calculator. Additional control sections  32  corresponding to keys available on calculators but not illustrated in FIG. 1F are also contemplated for inclusion on the template  18 . Further, control sections available on PC keyboards and/or personal digital assistants (PDAs), but not illustrated in FIG. 1F, may also be included on the template  18 . Also illustrated in FIG. 1F is a calculator image  46  displayed on the monitor  22 . The calculator image  46  can be similar to the calculator images commonly available in PC software. The calculator image  46  includes a display  48  where information is displayed to the user. The calculator image  46  can also optionally include a keypad with keys which are correlated to the control sections  32  included on the template  18 . The number and type of keys on the keypad can also differ from the control sections  32  included on the template  18 . 
     The control sections  32  can be used to control the display  48  on the calculator image  46 . Specifically, positioning the stylus in a control section  32  causes the processing unit  20  and/or the hardware unit  14  to carry out a function associated with the control section  32 . For instance, positioning the stylus  10  in the numerical control section  32  indicating the number 9 causes a number nine to appear in the display  48 . As a result, the control sections  32  on the template  18  can be used as the keypad of a calculator and the display  48  on the calculator image  46  can be used as the display  48  of the calculator. 
     The user interface  24  can be used to control the display  48  on the calculator image  46 . For instance, if the user interface includes a keyboard which is typically used with a PC, the keys on the keyboard can be used to control the display  48  on the calculator image  46 . For instance, pressing the number 2 on the keyboard can cause the number 2 to appear in the display  48 . Further, if the user interface includes a mouse or other cursor control device, the cursor can be aligned with the keys illustrated on the calculator image  46 . Clicking the mouse while the cursor is aligned with a particular key causes the function associated with that key to occur. 
     The calculator image  46  can include keys which do not correspond to any of the control sections  32  on the template  18 . These keys can perform functions which are not performed by positioning the stylus within any of the control sections on the template  18 . As described, the keys can be activated with a typical user interface. 
     The calculator image  46  need not always be visible to the user. For instance, the calculator image  46  can be manually called up onto the monitor  22  by positioning the stylus in the function control section  32  labeled “ON/C”. The calculator image  46  can also be automatically called up on the monitor  22  when the stylus is positioned in control sections  32  corresponding to the calculator functions other than the functional control section  32  labeled “OFF”. The calculator image  46  can be automatically withdrawn from the monitor  22  after a pre-determined period of time has elapsed. The calculator image  46  can also be manually withdrawn from the monitor  22  by positioning the stylus in the function control section  32  labeled “OFF”. 
     When the calculator image  46  is called up, the calculator image  46  can replace the monitor image area  36  on the monitor  22  or can appear over the monitor image area  36  as illustrated in FIG.  1 F. When the calculator image  46  appears over the monitor image area  36 , the user can switch between the monitor image area  36  and the calculator image  46  by using a user interface  24  such as a mouse to position a cursor on the calculator image  46  or the monitor image area  36 . As is known in Windows technology, when the cursor is positioned on the calculator image  46 , the calculator image  46  will be moved to the front so it is in full view. Similarly, when the cursor is positioned on the monitor image area  36 , the monitor image area  36  will be moved to the front so it is in full view. 
     It is noted that the image being formed on the writing surface may be simultaneously projected onto the same or a different surface, for example on an adjacent projectable surface, onto the writing surface (front or rear projection) or in a remote location. In this regard, the use of the template as a calculator as described above also allows the user to project a calculator onto an adjacent projectable surface and perform calculations without the user having to move away from the writing surface. 
     While the template is described above in terms of having calculator functions, it has already been noted that the template may perform a wide variety of functions and thus serve as a remote control device or user interface for the user. This enables the user to operate various applications, such as the calculator described above, or a webbrowser (e.g., to locate bookmarks, go back and forth between screen) without having to move away from the writing surface using the stylus and the template and display images of that application. This allows the user to readily transition between using the writing surface and the stylus as a transcription system and using a template and the stylus as a user interface for a variety of programs. 
     The hardware unit  14  or the processing unit  20  can optionally include a voice synthesizer which audibly describes the functions performed as the stylus is positioned in a control section  32 . For instance, when the stylus is positioned in the control section  32  labeled “2”, the voice synthesizer can audibly announce “two”. When the stylus is positioned in the control section  32  labeled “+”, the voice synthesizer can audibly announce “plus”. Further, when the stylus is positioned in the control section  32  labeled “=”, the voice synthesizer can announce “equals” and the result. For instance, if the stylus is sequentially positioned in the control sections  32  labeled “1”, “2”, “x”, “.”, “0”, “0”, “3” and “=”, the voice synthesizer would provide “one”, “two”, “times”, “point”, “zero”, “zero”, “three”, “equals”, “zero”, “point”, “zero”, “three”, “six”. As a result, the voice synthesizer can eliminate the need for a monitor  22  and a calculator image  46 . 
     Further, the display  48  can also be included on the hardware unit  14 . For instance, the hardware unit  14  can include a liquid crystal or LED display as are commonly available in calculators. The display can then be controlled by positioning the stylus in the control sections on the template  18  or by activating control switches on the hardware unit. 
     FIG. 1G illustrates another embodiment of a template  18  which is suitable for use with the transcription system. Although the previously illustrated control sections  32  are square or rectangular, the control sections can have shapes including, but not limited to, triangular, elliptical, octagonal, hexagonal and round as is illustrated in FIG.  1 G. FIG. 1G also illustrates the control sections  32  including icons or text which indicate to the user the function that will be performed by positioning the writing portion of the stylus within the perimeter of one of the control sections. Although the previously illustrated calibration marks are illustrated as being positioned along one edge of the template  18 , the calibration marks can be positioned anywhere on a template. Preferably, the calibration marks  40  are positioned with a maximum displacement between the calibration marks. As a result, the calibration marks can be positioned in opposing corners of the template  18  as illustrated in FIG.  1 G. 
     As illustrated in FIG. 1H, the writing surface  28  can also include a background image  50  which is either printed onto the writing surface or positioned over the writing surface. Alternatively, the background image  50  can be projected onto the writing surface. Since the writing surface can be constructed from transparent materials such as glass or plastic, the background image  50  can be projected onto the surface from either behind or in front of the writing surface. Suitable forms for the background image  50  include, but are not limited to, a spreadsheet as illustrated in FIG. 1H, blueprints, handwritten or typewritten text, notes, graphs, graphics, etc.. The background image  50  can be placed on a material which is physically attached to surface and used as the writing surface. Examples of materials on which a background image  50  may appear include paper, plastic sheets and other materials which can be written upon. The background image  50  can also be an image which is projected onto a writing surface  28 . For instance, the background image  50  can be an image projected onto the writing surface  28  from a front or rear projection system (e.g., a reflective or transmissive display). 
     As illustrated in FIG. 1H, when a background image  50  is used on the writing surface  28 , writing on the writing surface in combination with the background image  50  forms a composite image  52  which appears on the monitor  22 . The system can be calibrated so strokes written on the writing surface  28  are properly positioned relative to the background image  50  in the composite image  52  that is formed. For instance, when the background image  50  includes an image of a spreadsheet, an image written into a particular cell of the background image  50  appears in the same cells on the composite image  52  as illustrated in FIG.  1 H. 
     The background image  50  and the image upon the background image  50  can be created with the processing unit  20 , monitor  22  and user interface  24 . For instance, the image for the background image  50  can be a spreadsheet created with a program such as EXCEL. Other images for the background image  50  can be created with graphics programs such as VISIO, CAD programs, or other programs used to make documents. The image for the background image  50  can also be externally created. For instance, the image for the background image  50  can be blueprints which are scanned into the processing unit  20  via a scanner. 
     The system can include logic for converting the image for the background image  50  to an Image file. During conversion to the Image file, the logic adds calibration marks  40  to the image for the background image  50 . The Image file can then be printed on a conventional printer or on a printer which can print enlarged size sheets. 
     The background image  50  can be printed on paper or on a transparency suitable for projection from an overhead. A printed background image  50  can also be converted to a form suitable for projection such as a transparency for an overhead projector or a slide for a slide projector. 
     Once the background image  50  is positioned on the writing surface, a background image calibration may be required in order to determine the position of the background image  50  relative to the detectors  12 A,  12 B. To initiate the background image calibration, the user notifies the system that a particular background image  50  will be used in combination with a writing surface  28 . Once the system is notified, the user is prompted to contact the stylus with one or more calibration marks  40  having a predetermined physical relationship to the background image  50 . Contacting the calibration marks  40  with the stylus serves to identify the position of the background image  50  relative to the detectors  12 A,  12 B. Because the position of the stylus is also measured relative to the detectors, contacting the calibration marks  40  with the stylus permits a determination of the position of the stylus  10  relative to the background image. 
     In one embodiment of using a background image, illustrated in FIG. 1I, a background image  50 , such as an image from a webpage is projected onto a writing surface  28  (illustrated as a rear projection). Writing  54 , such as comments or modifications to the projected background image, are made relating to the projected background image by writing on the writing surface  28 , thereby forming a composite image comprising the projected background image  50  and the writing  54 . The composite image  52  of the projected background image  50  and the writing made on the writing surface can be displayed on a monitor  22 , stored into memory, and/or projected in another location. As can be seen from this embodiment, a variety of composite images can be formed which allow for a dynamic range of graphic presentations to one or more remote locations. 
     System Variations 
     In general, the transcription system records the written image  44  by detecting the position of the stylus  10  on the writing surface  28  at multiple times, each position detected serving to form a point on the monitor image  34 . By detecting the position of the stylus  10  at a sampling rate that is fast relative to the speed with which the stylus  10  is moved during writing, an image  34  corresponding to what has been written can be recorded and displayed in real time. As will be described in detail below, each point is determined based on the time that it takes for a position signal to travel between the stylus  10  and the first and second detectors  12 A,  12 B. This time is called the position signal&#39;s time of flight. 
     Several different system designs may be employed in order to determine a position signal&#39;s time of flight between the stylus  10  and the first and second detectors  12 A,  12 B. Several of these different system designs are described with regard to FIGS. 2A-2D. It is noted however that additional system configurations may also be envisioned and are intended to fall within the scope of the present invention. 
     FIG. 2A illustrates an embodiment where the stylus  10  includes at least one reference signal receiver  56  and a position signal transmitter  58 . Meanwhile, the first detector  12 A and the second detector  12 B each include a position signal receiver  60 . Located somewhere in the system is a reference signal transmitter  62 . In FIG. 2A, the reference signal transmitter  62  is included in the second detector  12 B. In other embodiments, the reference signal transmitter  62  can be included in the hardware unit  14 . 
     As illustrated in FIG. 2A, a reference signal  64  is transmitted to the stylus  10 . Receipt of the reference signal  64  by the stylus  10  triggers the stylus  10  to transmit a position signal  66 . The position signal  66  is propagated radially from the stylus  10  and received by the first detector  12 A and the second detector  12 B at a time that is dependent on the distance between the stylus  10  and each of the first detector  12 A and the second detector  12 B at the time that the position signal  66  is produced. Since the position signal  66  is transmitted at a known time after the reference signal  64  is transmitted, the time of flight of the position signal  66  to the first and second detectors  12 A,  12 B can be determined. 
     The hardware unit  14  receives position signals  66  from the first and second detectors  12 A,  12 B and controls the transmission of the reference signals  64  from the reference signal transmitter  62 . The hardware unit  14  uses the received position signals  66  to determine the time of flight of the position signal  66  from the stylus  10  to the first detector  12 A and the second detector  12 B. The time of flight is received by the processing unit  20  which includes logic for using the time of flight data to determine the position of the stylus  10  relative to the first detector  12 A and the second detector  12 B. The logic may employ a variety of methodologies for determining the position of the stylus  10  including, for example, triangulation or a look-up table containing different positions associated with different times of flight to the first and second detectors  12 A,  12 B. 
     A variety of reference signals  64  may be used. In general, the reference signal  64  should be at least as fast as the position signal  66  and is preferably significantly faster than the position signal  66 . When the reference signal  64  is significantly faster than the position signal  66  (e.g., speed of light vs. speed of sound), it is possible to disregard the time of flight of the reference signal  64  when determining the time of flight of the position signal  66 . In one embodiment, the reference signal  64  travels at the speed of sound and in another travels at the speed of light. In a particular embodiment, the reference signal  64  is a form of electromagnetic radiation, such as an infra-red (IR) or radio frequency (RF) signal. The position signal may also be ultrasound. 
     A variety of position signals  66  may be used. In one embodiment, the position signal  66  is ultrasound. In another embodiment, the position signal  66  is a form of electromagnetic radiation, preferably micro-impulse radar which yields an effective time of flight for electromagnetic signals. 
     FIG. 2B illustrates an alternative embodiment where the stylus  10  includes a position signal transmitter  58  and is physically attached to the hardware unit  14  by a wire  68 . Meanwhile, the first detector  12 A and the second detector  12 B each include a position signal receiver  60 . 
     As illustrated in FIG. 2B, a reference signal  64  is transmitted to the stylus  10  from the hardware unit  14  via the wire  68 . When the reference signal  64  is received, the stylus  10  transmits a position signal  66  which propagates radially from the stylus  10  and is received by the first detector  12 A and the second detector  12 B at a time that is dependent on the distance between the stylus  10  and the first detector  12 A and the second detector  12 B at the time that the position signal  66  is produced. Since the position signal  66  is transmitted at a known time after the reference signal  64  is transmitted, the time of flight of the position signal  66  to the first and second detectors  12 A,  12 B can be determined. 
     FIG. 2C illustrates an alternative embodiment where the stylus  10  includes a position signal transmitter  58  and the first detector  12 A and the second detector  12 B each include position signal receivers  60 . The stylus  10  also includes a reference signal transmitter  62  and the second detector  12 B includes a reference signal receiver  56  in addition to the position signal receiver  60 . 
     As illustrated in FIG. 2C, a reference signal  64  is transmitted by the stylus  10  to the second detector  12 B to signal that a position signal  66  is being transmitted or is about to be transmitted. The position signal  66  is received by the first detector  12 A and the second detector  12 B. Since the position signal  66  is transmitted at a known time after the reference signal  64  is transmitted, the time of flight of the position signal  66  to the first and second detectors  12 A,  12 B can be determined by the processing unit  20 . 
     In the embodiment illustrated in FIG. 2C, the reference signal  64  and the position signal  66  can be transmitted together for each point in the monitor image  34 . However, the position signal  66  can also be transmitted without the reference signal  64 . For instance, the reference signal  64  can serve to synchronize the timing of the stylus  10  and the hardware housing and/or the processing unit  20 . When the reference signal  64  serves as a synchronizing signal, the stylus  10  is configured to transmit a series of position signals  66  at a known time interval. The reference signal  64  indicates when the first position signal  66  in the series is transmitted. The hardware unit  14  includes a timer which is started after receiving the reference signal  64 . The first time of flight determination for a particular detector is made by measuring the time between starting the timer and receiving the position signal  66  at the particular detector. Since subsequent position signals  66  are transmitted at known intervals, the hardware housing and/or the processing unit  20  can include logic for determining when each subsequent position signal  66  is transmitted. As a result, the time of flight to a particular detector can be calculated by determining the time between when the position signal  66  is transmitted and when the position signal  66  is received at that detector without each time of flight needing a reference signal to obtain the measurement. 
     FIG. 2D illustrates yet another embodiment where the stylus  10  includes a position signal receiver  60  and a reference signal transmitter  62 . The first detector  12 A and the second detector  12 B include position signal transmitters  58  and reference signal receivers  56 . It is noted that this embodiment can be readily varied where the stylus  10  includes a reference signal receiver  56  and one or both of the first detector  12 A and the second detector  12 B include a reference signal transmitter  62 . 
     As illustrated in FIG. 2D, the first and second detectors  12 A,  12 B transmit different position signals  66  which can be distinguished by the position signal receiver(s)  60  on the stylus  10 . When the stylus  10  receives one or more of the position signals  66 , the stylus  10  transmits a reference signal  64  to confirm receipt of the position signal  66  and request that the next position signals  66  be sent. 
     System Variations Relating To Calibration 
     The systems described above may require calibration. For example, it may be necessary to determine a separation between detectors, a dimension of the writing area, a temperature adjacent the writing surface, a position of a template relative to a writing surface, and/or a position of a background image positioned on, printed on, or projected on a writing surface. 
     The displacement, L, between first and second detectors can be determined. The dimension of the writing area  38  can also be determined during calibration. For instance, the writing area height, H, writing area width, W, and writing area diagonal, D, are some of the dimensions which can be determined during calibration. Each of these dimensions are illustrated in FIG.  3 A. The position of the template  18  and each of the control sections  32  can also be determined during the calibration of the system. Different embodiments of the transcription system require that different combinations of these variables or none of these variables be determined during calibration. 
     FIG. 3B illustrates an embodiment which can automatically determine the first and second detector displacement, L. The first detector  12 A includes a reference signal receiver  56  and a position signal transceiver  70 . Examples of suitable position signal transceivers  70  include, but are not limited to, PZT, PVDF, electrostatic and piezoelectric or piezoceramic ultrasonic transceivers. 
     During calibration of the system, a reference signal  64  transmitted from a reference signal transmitter  62  included in the second detector  12 B is received at the reference signal receiver  56  included in the first detector  12 A. In response, a position signal  66  is transmitted from the position signal transceiver  70  in the first detector  12 A. The position signal  66  is received by the position signal receiver  60  of the second detector  12 B. The time of flight of the position signal  66  between the first and second detectors  12 A,  12 B can be multiplied by the speed of sound to determine L. When the system is not being calibrated, the position signal transceiver  70  works as a position signal receiver  60 . In another embodiment, the position signal transceiver  70  can be replaced with a position signal transmitter  58  and an independent position signal receiver  60 . 
     FIG. 3C illustrates another embodiment including features for system calibration. The first detector  12 A includes a calibration mark  40 . During calibration, the user is prompted by the computer to contact the stylus  10  within the calibration mark  40 . Upon contact of the stylus  10  with the calibration mark  40 , the stylus transmits a position signal  66 . The position signal  66  is received at the position signal receiver  60  included in the second detector  12 B. The time of flight of the position signal  66  between the first and second detectors  12 A,  12 B is multiplied by the speed of sound to determine the first and second detector displacement, L. 
     As discussed above, the processing unit  20  may optionally produce an image on the monitor  22  to guide the user through the calibration. For instance, the processing unit  20  can create an image  42  of a stylus  10  contacting the calibration mark  40  on an image of the first detector  12 A. In response, the user can contact the stylus  10  with the calibration mark  40  of the first detector  12 A as illustrated. The user can also be prompted to contact the stylus  10  to the calibration marks  40  by commands on the monitor  22  through feedback obtained from a multi-media computer. For instance, “Touch stylus to left detector.” can appear on the monitor  22 . The command can also take the form of an audible message. 
     The first and second detectors can be included in a detector assembly  72  as illustrated in FIG.  3 D. The detector assembly  72  includes a coupling member  74  attached to each of the first and second detectors  12 A,  12 B. The coupling member  74  keeps the first and second detectors  12 A,  12 B at a known displacement. As a result, the first and second detector displacement, L, is a known constant which does not need to be determined during the calibration. 
     As illustrated in FIG. 3E the detector assembly  72  can be positioned along the side of the writing area  38 . This arrangement of the first and second detectors  12 A,  12 B can be advantageous as it keeps the wires on only one side of the writing surface  28  rather than needing to be guided around the periphery of both sides of the writing surface  28 . Further, the first and/or second detectors  12 A,  12 B can be designed to receive position signals  66  from a 180 degree range of directions called the reception range. The 180 degree reception range allows the writing area width, W, and the writing area height, H, to extend beyond the first and second detector displacement, L. 
     As also illustrated in FIG. 3E, the position of the template  32  relative to the detector assembly can be determined by the system by contacting two different locations of the template (dark boxes) whose location relative to the overall template  32  is known by the system. 
     In another embodiment, the system calibrates itself to correct for the effect of temperature changes on the speed of ultrasound signals in the transcription system. Temperature sensors may optionally be incorporated into the stylus, template and/or positioned adjacent one or more of the detectors. According to this embodiment, the temperature adjacent the writing surface is periodically measured and the time of flight calculations are adjusted in view of the measured ambient temperature. By performing this type of calibration periodically, changes in temperature conditions, for example due to whether sunlight is impacting upon the writing surface, can be addressed. 
     The Stylus 
     One or more styluses may be used with the transcription system. FIG. 4A illustrates an embodiment of a stylus  10  which can be used with the transcription system illustrated in FIG.  2 A. As illustrated, the stylus  10  includes a stylus housing  76  and a writing element  78 . Examples of suitable writing elements  78  include, but are not limited to, an inkwell, chalk, pencil, pencil lead, pen and a marker such as a SANFORD EXPO. The stylus housing  76  includes a tip end  80  with a position signal transmitter  58  adjacent the end. The stylus housing  76  as illustrated also includes activation electronics  82 , implement electronics  104 , and a plurality of reference signal receivers  56 . The stylus housing  76  is also capable of housing a power source  84  which is preferably removably attachable to the stylus. 
     In FIGS. 2A,  2 C and  2 D, the reference signal transmitters  62  or reference signal receivers  56  are illustrated as being positioned at an upper end of the stylus, however, the reference signal transmitters  62  or reference signal receivers  56  can be positioned at the tip end  80  of the stylus  10  as illustrated in FIG.  4 A. Reference signal transmitters  62  or reference signal receivers  56  can also be included as a ring of piezoelectric material  86  extending around the circumference of the stylus  10 . The ring of material can be constructed from any material known to transmit the reference signal. 
     As illustrated in FIG. 4B, the stylus housing  76  may be designed such that the writing element  78  is removable from the stylus housing  76 . As illustrated, the stylus housing  76  may include a removable member  88  which is attachable and detachable to an end of a sleeve  90 . As illustrated, sleeve  90  defines a volume  92  within which the writing element  78  may be positioned and the removable member  88  serves to maintain the writing element  78  within the sleeve  90 . When the writing instrument is replaced, the tip  94  of the replacement writing instrument is inserted through the stylus housing  76  and into the tip end  80  of the stylus  10 . The removable member  88  is placed on the stylus  10  so the rear  96  of the writing instrument is in contact with the activation electronics  82 . 
     As illustrated in FIG. 4C, the stylus housing  76  may include a first member  98 A which is attachable and detachable to a side of a second member  98 B. Detaching the first member  98 A from the side of the second member  98 B provides easy access to the writing element  78  and the power source  84 . By enabling the writing element  78  to be readily removable, the writing element  78  can be replaced when writing media contained in the element is exhausted or a different writing media (type or color) is desired. Similarly, enabling the power source  84  to be readily removable permits the power source  84  to be replaced when the power begins to run low. 
     As illustrated in FIGS. 4C and 4D, the stylus housing  76  may include an aperture  100  which allows a user to rotate the writing element  78  about its longitudinal axis without having to open or otherwise disassemble the stylus housing  76  and without having to remove the writing element  78  from the stylus housing  76 . As illustrated, some writing elements include a tip which is not symmetrical about the longitudinal axis of the writing element, such as a wedge shaped tip of a marker. In such instances, it may be desirable to periodically alter the angular positioning of the tip of the writing element relative to the stylus housing  76 . This may be accomplished in this embodiment by rotating the writing element while it is in the housing through the aperture  100  without having to remove or disassemble the stylus. 
     As also illustrated in FIG. 4A, the stylus housing  76  may optionally include a sensor  102  adjacent the end of the stylus housing  76  out of which the writing element  78  extends which serves to detect if the writing element  78  is out of writing media. For example, the sensor may be used to detect a water content or another solvent content of the portion of the writing element extending from the housing, thereby alerting a user when the writing element is out of ink or has dried out and needs to be replaced. An example of a sensor is a pair of contacts positioned at the end of the stylus housing. In operation, a current can be passed through the tip of the writing element. The tip of certain writing element will conduct varying amounts of current depending on the amount of writing media which remains within the stylus. Accordingly, the stylus can include logic for monitoring the current through the tip to identify the amount of media remaining in the writing element When the sensor detects that the amount of media is below a threshold, the stylus can provide a low media signal encoded into a reference signal or a position signal. Upon detecting the low media signal the hardware unit can activate a particular indicator or can provide a second low media signal to the processing unit which can respond accordingly. 
     It is preferred that at least a portion of the stylus housing  76  is clear or opaque such that it is possible to see the writing element  78  within the housing. This allows the user to observe the color of the writing element  78  without having to open the housing or remove the writing element  78 . In certain instances, for example when chalk, graphite or a liquid ink reservoir is used in conjunction with the writing element, it is possible to observe how much writing media is remaining. 
     The activation electronics  82  can include a contact switch which indicates when the stylus  10  is being used to write. The contact witch typically works based on pressure being exerted between the stylus  10  and a writing surface  28 . In operation, the stylus  10  is held such that the tip  94  of the writing instrument is contacted with the writing surface  28 . The pressure of the writing instrument on the writing surface  28  closes the contact switch to activate a circuit within the implement electronics  104 . 
     When the circuit within the stylus housing  76  is activated, an activation signal is provided to the system to indicate that the stylus  10  has been contacted with the writing surface  28 . The propagation of reference and position signals  66  can be initiated in response to the activation signal. The activation signal may be a position signal  66  or a reference signal  64  transmitted from the stylus  10 . Similarly, when the implement electronics  104  is deactivated by lifting the stylus  10  off the writing surface  28 , a deactivation signal may be transmitted to the system. The system can also detect when the implement electronics  104  has been deactivated by detecting that a position signal  66 , or reference signal  64 , has not been transmitted from the stylus  10  for some predetermined period of time. 
     The activation electronics  82  can optionally include a pressure sensor which measures the pressure exerted between the stylus  10  and the writing surface  28  called the exerted pressure. Examples of pressure sensors which may be used include, but are not limited to strain sensors, piezoelectric elements or linear resistive strips. The activation electronics  82  can produce a signal indicating the exerted pressure. The signal can be received within the implement electronics  104  and can serve to activate the implement electronics  104 . The implement electronics  104  can include logic for encoding a pressure signal which indicates the degree of exerted pressure into a reference signal  64  or a position signal  66  transmitted from the stylus  10 . Whether the pressure signal is encoded into the reference signal  64  or the position signal  66  depends on whether the stylus  10  includes a position signal transmitter  58 , a reference signal transmitter  62 , or both. 
     Additional signals can be encoded into position signals or reference signals by varying the characteristics of the signal. For instance, to encode an additional signal into a reference signal, the value of the additional signal can be digitized and sent as a series of bits in the reference signal. To encode an additional signal into a position signal, the position signal can be transmitted with varying frequencies or durations which are a function of the additional signal value. 
     The pressure signal can be received by the hardware unit  14  or the processing unit The hardware unit  14  or the processing unit  20  can include logic which can identify the pressure signal and interpret the pressure signal to determine the amount of pressure being exerted on the stylus  10 . The hardware unit  14  or the processing unit  20  can also include logic for adjusting the width of each stroke on the monitor image  34  in response to the exerted pressure. For instance, when the pressure signal indicates that large pressure is being exerted, the width of the stroke on the monitor image  34  can be increased and when the exerted pressure is low, the width of the stroke on the monitor image  34  can be decreased. As a result, the monitor image  34  is created to more closely resemble the written image  44 . 
     The implement electronics  104  can also optionally include a power monitoring device which monitors the amount of power remaining in the power source  84 . Examples of power measuring devices which may be used include, standard power monitoring circuits and can be included in some microcontrollers. When the available power falls below a threshold level, a power signal can be encoded into a reference signal  64  or a position signal  66  transmitted from the stylus  10 . The power signal can be received by the hardware unit  14  or the processing unit  20 . The hardware unit  14  or the processing unit  20  can include logic which can identify the power signal. Once the power signal has been identified, the user can be notified of the low power status by a message on the monitor  22  or by an indicator on the hardware unit  14 . An example of an indicator (not shown) on the hardware unit  14  may be an LED which flashes once the power signal has been received. 
     The implement electronics  104  can also include logic for producing an identifier signal which is unique to the type of the stylus  10  being used The identity signal can be encoded into a reference signal  64  or a position signal  66  transmitted from the stylus  10 . The hardware unit  14  or the processing unit  20  can include logic which can identify the identity signal and interpret the identity signal to determine the type and accordingly the characteristics of the stylus  10  from the identity signal. The characteristics of the stylus can include color, line, width, and line pattern. 
     The identifier signal can be transmitted when the implement electronics  104  are first activated or each stylus  10  can constantly transmit signals which are unique to that particular type of stylus  10 . The identifier signal can be received within the hardware unit  14  or the processing unit  20  and used to identify the particular stylus  10  being used to write upon the writing area  38 . Once the stylus  10  has been identified, the monitor image  34  is created with characteristics which correlate to the identified stylus  10 . For instance, the stroke on the monitor image  34  can have a color matching the color of the stylus  10  being used to write on the writing surface  28  can have a stroke width matched to the width of the stylus  10 . 
     When the stylus transmits an identifier signal which is identified with a particular color, the stylus housing  76  can include a visible identifier which indicates to a user the color of the strokes which will appear on the monitor image  34  when that stylus  10  is used. For instance, the stylus housing can be 50% transparent and 50% red in color to indicate that use of the stylus will cause red colored strokes to appear on the monitor. Of course, the transcription system can include logic for changing the color of a stroke on the monitor after the stroke has been made. 
     When the stylus transmits an identifier signal which is identified with a particular characteristics, the stylus housing  76  can be designed so it will accept only writing implements with the particular characteristics. For instance, if a stylus housing transmits an identity signal which is identified with the color red, the stylus housing and writing implements can be designed so the stylus housing will not accept writing implements which are not red. One method for achieving this correlation of stylus housings with writing implements is to design the writing implements with particular characteristics so the writing implements have a geometry which is unique to the particular characteristics. For instance, blue writing implements can have a unique length, unique diameter or unique cross sectional shape such as round, hexagonal, octagonal, oval, etc.. The stylus housings  76  which accept writing implements with particular characteristics can have sleeves defining volumes  92  which are complementary to the unique writing implement geometry. For instance, if blue pens have a hexagonal cross section, the volume  92  within the correlated stylus housing can have a hexagonal cross section. 
     The implement electronics  104  can also include logic for responding to inquiry signals from the hardware unit  14  or the processing unit  20 . The inquiry signal can be coded into a reference signal  64  which is transmitted from a first or second detector  12 A or  12 B. The stylus  10  receives the reference signal  64  and logic within the implement electronics  104  recognizes the inquiry signal. The logic can also interpret the inquiry signal as inquiring whether the stylus  10  is a particular type of stylus  10 . The logic in the implement electronics can cause the position signal  66  to be withheld or transmitted based on whether the stylus  10  matches the type of stylus inquired about. The hardware unit  14  or the processing unit  20  can include logic for interpreting the transmission or lack of transmission of the position signal  66 . 
     As also illustrated in FIG. 4A, the stylus  10  includes reference signal receivers  56 . These receivers are preferably evenly spaced around the stylus  10  so that reference signals  64  can be received from any angle relative to the stylus  10 . In a preferred embodiment, the reference signal receiver  56  is an IR signal receiver. An example of an IR receiver that may be used includes, but is not limited to, a photo diode. The reference signal  64  can also be an RF signal. 
     As also illustrated in FIG. 4A, the stylus  10  includes a position signal transmitter  58 . In one embodiment, the position signal transmitter  58  is an ultrasound transmitter. Examples of ultrasound transmitters that may be used include, but are not limited to, Polaroid L Series ultrasonic emitters, cylindrical polyvinylidene fluoride (PVDF) rings and similar piezotransducing elements. An example of a position signal  66  includes, but is not limited to, a 40 kHz signal emitted for approximately 0.7 ms. 
     FIG. 4C illustrates an embodiment of the stylus  10  which can be used with the transcription system illustrated in FIG.  2 B. The implement electronics  104  is coupled to the system via an electrical wire  68 . As a result, the reference signal  64  can be transmitted to the stylus  10  via the wire  68 . The position signal  66  is transmitted from the position signal transmitter  58  in response to receiving the reference signal  64 . 
     The stylus  10  can also be adapted to be used in a transcription system such as the one illustrated in FIG.  2 C. For example, the stylus  10  can include a reference signal transmitter  62  and a position signal transmitter  58 . The detectors  12 A,  12 B can be modified to include a reference signal receiver  56  and a position signal receiver  60 . 
     The stylus  10  can also be adapted to be used in a transcription system such as the one illustrated in FIG.  2 D. For example, the stylus  10  can include a reference signal transmitter  62  and a position signal receiver  60 . The detectors  12 A,  12 B can be modified to include a position signal transmitter  58 . A reference signal receiver  56  is also provided in the system and may optionally be incorporated into one of the detectors  12 A,  12 B. 
     The stylus can include a cap for covering a portion of the writing element which extends outside of an end of the stylus housing and is used to write upon a writing surface. The cap may optionally be clear in order to allow the user to observe the color of the writing element without having to remove the cap. The cap may also optionally be sized to fit over a position signal transmitter or position signal receiver positioned adjacent an end of the stylus housing out of which the writing element extends. The stylus housing may optionally include a cap holding mechanism to which the cap may be attached when the stylus is in use. 
     An example of a stylus cap is illustrated in FIG.  4 D. The cap  106  is configured to be coupled with the stylus  10  as illustrated in FIGS. 4C and 4E. The cap  106  can also configured to be coupled with a back end the stylus as illustrated in FIG.  4 D. Accordingly, during operation of the stylus, the cap  106  can be stored on the back of the stylus in order to prevent loss of the cap  106 . The cap  106  can serve to protect the tip of the stylus  10  or the writing element  78  when the stylus  10  is not in use. The cap can also serve to prevent certain types of writing elements  78 , such as markers, from drying out from exposure to air. 
     FIG. 4F is a cross section of the stylus housing  76  coupled with the cap. The cap  106  includes a position signal transmitter/receiver accommodation area  108 . The position signal transmitter/receiver accommodation area  108  has a volume which is sufficient for a position signal transmitter  58  or a position signal receiver  60  to fit within the cap without being in contact with the cap  106 . As a result, the position signal transmitter/receiver accommodation area  108  serves to protect the position signal transmitter  58  or position signal receiver  60  when the cap is coupled with the stylus housing  76 . 
     The cap  106  may include stylus contact points  110  as illustrated in FIG. 4F and 4G. The stylus contact points  110  are in contact the stylus housing  76  when the cap  106  is coupled with the stylus housing  76 . The stylus contact points  110  limit the distance that the cap  106  can be pushed onto the stylus housing  76  to prevent damage to the stylus  10  and/or the writing element  78 . 
     As illustrated in FIG. 4G, the stylus contact points  110  can contact the tip end  80 . When the stylus contact points  110  contact the tip end  80 , he volume of the position signal transmitter/receiver accommodation area  108  is reduced. Reducing the volume also reduces the amount of air within the position signal transmitter/receiver accommodation area  108 . As a result, the amount of moisture which can be withdrawn from certain writing elements  78  is reduced also reducing the opportunity for certain writing elements  78  to become dried out. 
     A variety of mechanisms can be utilized for removably attaching the stylus cap to the housing. For example, the cap may include a gripping sleeve section  112  which contacts the stylus housing  76 . The gripping sleeve section  112  has enough length that the friction between the gripping sleeve section  112  and the stylus housing  76  keeps the cap  106  in place on the stylus  10 . 
     As illustrated in FIG. 4H, the stylus housing  76  can include a stylus ridge  116  and the cap  106  can include a cap ridge  114 . The diameter of the cap ridge  114  is smaller than the diameter of the stylus ridge and the cap  106  is constructed from a flexible materials which pen and marker caps are traditionally constructed from. When the cap  106  is pushed onto the stylus  10 , the diameters of the cap ridge  114  and the stylus ridge  116  prevent the cap  106  from sliding on. However, when sufficient pressure is applied to the cap  106 , the cap  106  deforms enough for the cap ridge  114  to slide past the stylus ridge  116 . In this position, pressure is also required to remove the cap  106  from the stylus  10 . As a result, the cap  106  remains in place on the stylus  10  until the user applies the pressure necessary to remove the cap  106 . 
     The above cap embodiments are advantageous because traditional cap designs frequently rely on friction between the stylus neck  118  and the cap  106  to keep the cap  106  in place. However, such a cap design could damage a position signal transmitter  58  positioned on the stylus neck  118 . Further, traditional caps do not include the volume required to accommodate the position signal transmitter  58 . 
     FIGS. 4K and 4L illustrate further alternative embodiments of styluses that may be used with the system of the present invention. These styluses are designed to be used with a removeable, disposable writing element which includes its own power source for powering the operation of the stylus. These embodiments obviate the need for a separate power source  84  and a separate space in the stylus housing for a power source  85 , as shown in FIG.  4 C. This allows the stylus design to be made smaller and more ergonomic. In particular, as can be seen in FIGS. 4K and 4L, the styluses have a narrower design which allows the styluses to better approximate the size and feel of a standard whiteboard marker. 
     FIG. 4K illustrates a stylus embodiment where the stylus electronics are positioned toward a distal end of the stylus adjacent the tip. As illustrated, the stylus includes a housing comprised of a proximal body  111 , a distal body  113 . A removeable, disposable writing element  115  is sized to fit within the stylus housing. The writing element  115  includes a power source  117  and power source contacts  119 . 
     Included on the proximal body  111  is an exterior pen housing  121  which is preferably clear to show the color of the writing element being used. Also included on the proximal body  11  is a groove  123  for holding the stylus cap. Power source contacts and electrical traces (not shown) are also included in the proximal body  111  for delivering power from the power source  117  on the writing element  115  to electronics on the distal housing body  113 . 
     Included on the distal body  113  is a piercing element  125  for delivering writing media from the writing element  115  to a stylus tip  127 . It is noted that the distal body  113  may optionally include a bore (not shown) through which a writing tip from the writing element  115  can pass and be positioned where the stylus tip  127  is shown. Also included in the distal body is a signal transmitter  129 , preferably a transducer, electronics  131  for operating the stylus, and threading  133  for connecting the proximal body  111  to the distal body  113 . As also illustrated, a cap  135  is provided which is sized to fit over the stylus tip  127  and the signal transmitter  129 . 
     FIG. 4L illustrates a stylus embodiment where an elongated writing element is employed which allows the diameter of the stylus to be further reduced. As illustrated, the stylus includes a housing  137  with a bore  139  through a middle of the housing. An elongated removeable, disposable writing element  141  is sized to fit within the bore  139  in the stylus housing  139 . The writing element  141  includes a power source  143  and power source contacts  145 . The stylus housing  137  also includes contacts  147  which are positioned to contact the power source contacts  145 . Also included on the stylus housing is a stylus tip  149 , a signal transmitter  151 , preferably a transducer, and electronics  153  for operating the stylus. It is noted that the housing  139  may optionally include a bore (not shown) through which a writing tip from the writing element  141  can pass and be positioned where the stylus tip  149  is shown. As also illustrated, a cap  155  is provided which is sized to fit over the stylus tip  149  and the signal transmitter  151 . 
     The Eraser 
     FIG. 5A illustrates an eraser  16  which may be used in a system according to the present invention. The eraser  16  illustrated includes a holding surface  120 , an eraser pad  122 , a position signal transmitter  58 , a reference signal receiver  56 , activation electronics  82  and implement electronics  104 . It is noted that this eraser  16  is designed for use in a transcription system such as the one illustrated in FIG.  2 A. However, the eraser  16  can be modified, as described above with regard to the stylus  10 , for use with different transcription systems. 
     In operation, the eraser  16  is positioned such that the eraser pad  122  is pushed against the writing surface  28 . The eraser pad  122  is constructed from a material which erases the writing element media from the writing surface  28 . For instance, when the writing element  78  is a white board marker, the eraser pad  122  can be a typical white board eraser material. As a result, contact between the eraser pad  122  and the writing surface  28  can serve to erase a portion of the writing image from the writing area  38 . 
     The activation electronics  82  on the eraser  16  can include a contact switch. The pressure of the eraser pad  122  on the writing surface  28  drives the eraser pad  122  against the contact switch closing the contact switch and activating a circuit within the implement electronics  104 . Activating the implement electronics  104  can serve to signal the eraser&#39;s  16  operation to the hardware unit  14  and/or the processing unit  20  in a similar manner as discussed with respect to the stylus  10 . 
     When the implement electronics  104  are activated, a reference signal  64  received at one of the reference signal receivers  56  triggers a position signal  66  to be transmitted from the position signal transmitter  58 . The reference signal receivers  56  are preferably evenly spaced around the eraser  16  so a reference signal  64  can be received from different angles around the eraser  16 . The reference signal receivers  56  and the position signal transmitter  58  can be similar to the reference signal receivers  56  and the position signal transmitter  58  used in the stylus  10 . 
     The signal transmitted by the position signal transmitter  58  on the eraser  16  can optionally be different from the signal transmitted by the position signal transmitter  58  on the stylus  10 . The hardware unit  14  and/or the processing unit  20  can then distinguish that the signal being received is from the eraser  16  as opposed to the stylus  10 . When the transcription system detects that it is receiving signals from the eraser  16 , the transcription system erases the monitor image  34  according to the position of the eraser  16  on the writing surface  28 . 
     The processing unit  20  detects the position of the position signal transmitter  58  on the eraser  16 . However, the portion of the written image  44  which is erased is the portion of the written image  44  in contact with any portion of the eraser pad  122  and not simply the position of the position signal transmitter  58 . Accordingly, the processing unit  20  includes logic which accounts for the portion of the written image  44  actually contacted by the eraser pad  122 . The processing unit  20  can be used to calculate an approximate eraser area  124  which matches the eraser pad footprint  126  as illustrated in FIG.  5 B. As the eraser  16  is moved about the writing surface  28 , the portion of the monitor image  34  which falls within the approximate eraser area  124  is erased from the monitor image  34 . The size of the approximate eraser area  124  can be adjusted so it matches the actual size of the eraser pad footprint  126 . Similarly, the approximate eraser area  124  can be calculated to have different shapes which match the shape of the eraser pad footprint  126 . 
     The activation electronics  82  and the implement electronics  104  in the eraser  16  can perform many of the same functions as the activation electronics  82  and the implement electronics  104  in the stylus  10  in addition to the functions described above. For instance, the implement electronics  104  can include logic for transmitting an identity signal and/or low pressure signals encoded into a reference signal. Further, the implement electronics  104  can include logic for responding or not responding to inquiry signals encoded into reference signals  64 . 
     As illustrated, the eraser pad  122  may be sized to be a little smaller than the perimeter of the eraser. This sizing of the eraser pad  122  serves to prevent the user from using an edge of the eraser to erase with since erasing using an edge of the eraser may not cause the contact switch on the eraser to be depressed and erasing movement to be detected. This sizing of the eraser pad thus forces the user to place the eraser pad surface parallel to the writing surface in order to erase. 
     Detectors 
     FIG. 6A illustrates an embodiment of a detector  12 B which may be used with the transcription system illustrated in FIG.  2 A. The detector  12 B includes a detector housing  128 , detector electronics  130  and a position signal receiver  60  and a reference signal transmitter  62 . The reference signal transmitter  62  is preferably positioned in an upper surface  132  of the detector housing  128 . An example of an ultrasound receiver that may be used is the Polaroid L Series Ultrasonic Receiver. An example of a reference signal transmitter  62  that may be used is an IR transmitter such as an photo diode or an RF transmitter such as an FM transmitter. The position signal receiver  60  may be coupled to the hardware unit  14  through a wire  68  connection (or a wireless connection) in order to communicate to the hardware unit  14  when position signals  66  are received by the detector  12 B. 
     As illustrated in FIG. 6B, a lower surface  134  of the detector housing  128  includes one or more attachment mechanisms  136  for removably attaching the detector housing  128  to the writing surface  28 . Examples of suitable attachments mechanisms include, but are not limited to, suction cups, magnets, VELCRO or a refreshable contact cement. It is also envisioned that mounting brackets may also be attached to the writing surface  28  which may obviate the need for an attachment mechanism. 
     The detector  12 B can be converted to detector  12 A for use with the system of FIG. 2A by removing the reference signal transmitter  62 . The detector  12 B may also be adapted for use with the transcription system of FIG. 2B by removing the reference signal transmitter  62 . 
     The detector  12 B may also be adapted for use with the transcription system of FIG. 2C by replacing the reference signal transmitter  62  with a reference signal receiver  56 . Examples of reference signal receivers  56  that may be used include, but are not limited to, a photo diode. 
     The detector  12 B may also be adapted for use with the transcription system of FIG. 2D by replacing the reference signal transmitter  62  with a reference signal receiver  56  and by replacing the position signal receiver  60  with a position signal transmitter  58 . 
     FIG. 7A illustrates another embodiment of detectors  12 A,  12 B that may be employed. The first or second detector  12 A,  12 B includes a reflecting surface  138  attached to a frame  140  which may serve as a shielding element. The reflecting surface  138  has a parabola shaped profile. The parabola is rotated 180 degrees about the parabola&#39;s focus to give the reflecting surface  138  a semi-circular footprint  142 . The reflecting surface  138  can be constructed from any material which will reflect the position signal  66 . In operation, the detectors  12 A,  12 B are positioned so the reflective surface extends into the writing area  38 . The shape of the reflecting surface  138  provides the reflecting surface  138  with about a 180 degree reception range, i.e., the reflecting surface  138  will reflect positions signals  66  transmitted from a range of 180 degrees. As a result, the detectors  12 A,  12 B can be positioned at a corner of the writing area  38  or along an edge of the writing area  38 . 
     FIG. 7B is a side view of the detectors  12 A,  12 B illustrated in FIG. 7A. A position signal receiver  60  positioned at the focal point of the parabola. An example of a position signal receiver  60  that may be used is the L-series manufactured by Polaroid. The parabolic shape causes position signals  66  traveling at right angles to the frame  140  to be reflected into the position signal receiver  60 . As a result, the reflecting surface  138  can serve to concentrate the position signals  66  and increases the opportunity for a position signal  66  to be received by the position signal receiver  60 . A suitable height of the position signal receiver  60  above the writing surface  28  includes, but is not limited to, approximately 1.7 inches. A suitable radius for the footprint of the reflecting surface includes, but is not limited to, approximately 1.8 inches. A suitable equation for defining the shape of the parabola includes, but is not limited to, y≈1.3x 2 . 
     The reflecting surface  138  can be designed to receive position signals  66  from varying angles. For instance, the reflecting surface  138  can have a parabola shaped profile which is rotated about 90 degrees about the parabola&#39;s focus as illustrated in FIG.  7 C. As a result, the reflecting surface has a 90 degree range of reception. The frame  140  can act as a filter by screening signals from outside the reception range and accordingly outside the writing area  38 . A detectors  12 A,  12 B having a 90 degree range of reception can be positioned at a corner of the writing area  38 . 
     FIG. 7D illustrates a detector assembly  72  with the hardware unit  14  mounted on the coupling member  74 . A cable  144  configured to be coupled with the processing unit  20  extends from the hardware unit  14 . The cable  144  can be permanently coupled with the hardware unit  14  or can be removably coupled with the hardware unit  14  via a serial port. In operation, the coupling member  74  is attached to the writing surface  28  via the attachment mechanisms. The coupling member  74  can be attached along the top, bottom or side of the writing surface  28 . Since the hardware unit  14  is positioned adjacent the writing surface  28 , the reference signal transmitter  62  or the reference signal receiver  56  can be included on the hardware unit  14 . Although the detectors  12 A,  12 B illustrated in FIG. 7A are shown as the detectors of FIGS. 6A-6B, the detectors of FIGS. 7A-7C can be substituted. 
     FIGS. 7E and 7F illustrate a detector assembly  72  with a coupling member serving as the hardware unit  14  by housing the electronics performing the functions associated with the hardware unit  14 . The attachment mechanisms  136 , the first detector  12 A and the second detector  12 B can be removably coupled with the coupling member  74  or can be integral with the coupling member  74 . The coupling member  74  can be constructed from a first member  146  and a second member  148 . The first member  146  can be coupled to the second member  148  by a hinge  150  extending through a vertical side of the coupling member  74 . As illustrated in FIG. 7G, the hinge  150  permits the coupling member  74  to adopt two or more configurations. A distance between the first and second detectors can change in at least two of the configurations. As illustrated in FIGS. 7E and 7F, in one configuration, the detector assembly  72  adopts a configuration where the displacement between the detectors is known. As illustrated in FIG. 7G, the detector assembly  72  can adopt a second configuration where the first and second detector are adjacent to one another. The second configuration can place the detector assembly  72  in a more compact form which is suitable for transporting the detector assembly  72 . 
     To facilitate the formability of the detector assembly  72 , the electronics can be positioned primarily within the first or second member  146 ,  148 . Flexible wiring can pass through or in proximity of the hinge  150  to permit electrical communication between the first member  146  and the second member  148 . For instance, the signals from the second detector  12 B coupled with the second member  148  can be communicated with the electronics positioned primarily in the first member via flexible wires passing through the hinge  150  or in proximity to the hinge  150 . 
     As illustrated in FIG. 7H, the hinge  150  can also extend through a horizontal side of the coupling member  74 . The detector assembly  72  can also include a third member  152  and a second hinge  154  as illustrated in FIG.  7 I. The first and second hinges  150 ,  154  permit the detector assembly  72  to adopt a first configuration and a second configuration. 
     The coupling member  74  can include releasable locking mechanisms for locking the coupling member  74  into the first or second configuration. The locking mechanism can be included in the hinge itself or on opposing portions of the first and second members  146 ,  148  which come into contact when the coupling member  74  is in a desired position. The hinge can also provide enough friction that the coupling member  74  remains in a particular position once the coupling member  74  is moved into the particular position. 
     As illustrated in FIG. 7J, the detector assembly  72  can be capable of telescopic expansion where it includes a second member  148  which fits slidably within the first member  146 . The slidability of the second member within the first member  146  permits the detector assembly  72  to adopt a first configuration and at least one second configuration. As illustrated in FIG. 7K, the first member  146  includes a blocking structure  156  and a first flange  158  while the second member  148  includes a second flange  160 . When the second member  148  is slid into the first member  146 , the blocking structure  156  and the second flange  160  come into contact to limit the inward displacement of the second detector  12 B. The second flange  160  contacting the blocking structure can indicate that the coupling member  74  is in a position suitable for transportation. When the second member  148  is withdrawn from the first detector  12 A, the second flange  160  contacts the first flange  158  to prevent the second member  148  from being pulled out of the first member  146 . The contact of the first flange  158  and the second flange  160  can indicate that the coupling member  74  is in a position suitable for operation of the transcription system. 
     The detector assembly  72  illustrated n FIGS. 7J and 7K can include a sensor system for automatically determining the displacement, L, between the detectors. For instance, the first or second members  146 ,  148  can include a resistive strip (not shown). The opposite member can include a contact which touches the resistive strip at different locations depending on the position of the first member  146  relative to the second member  148 . The resistive strip and the contact can be in electrical communication with the hardware controller. The hardware controller can complete a circuit through the contact and the resistive strip. The resistance in the circuit varies depending on the position of the contact relative to the resistive strip. Since the position of the contact relative to the resistive strip depends on the position of the first member  146  relative to the second member  148 , a relationship between the detector displacement, L, and the resistance in the circuit can be determined. By using this relationship, the displacement, L, between the detectors can be determined from the resistance in the circuit. As a result, the coupling member of FIGS. 7K and 7J can have a variable L which can be automatically determined and does not need to be calculated during calibration. 
     The coupling member  74  illustrated in FIGS. 7J and 7K can also include one or more releasable locking mechanisms. The one or more locking mechanisms can be used to lock the first and second members  146 ,  148  relative to one another once the user has moved them into a desired position. 
     As illustrated in FIGS. 7L, the detector assembly  72  can have a first configuration where the first and second detectors  12 A,  12 B are at a known displacement and a second configuration where the first and second members  146  and  148  are detached from one another. The first configuration can be formed by inserting a portion  162  of the first member  146  into an opening  164  in the second member  148 . Conversely, the second configuration can be formed by withdrawing the portion  162  of the first member  146  from the second member  148 . The detector assembly  72  can include a releasable locking mechanism which serves to retain the detector assembly  72  in the first configuration until the user chooses to detach the first member  146  from the second member  148 . 
     Electrical communication between the first and second members  146 ,  148  can be achieved by including electrical leads on the first and second members  146 ,  148  which are positioned to be in contact with one another when the first and second members are attached to one another. Alternatively, a cable can be removably attached to the first and second members  146 ,  148 . When the first and second members  146 ,  148  are detached, the cable can be detached from one or both of the first and second members  146 ,  148  in order to completely detach the first and second members  146 ,  148 . 
     FIG. 7M illustrates a user actuated attachment mechanism  136  which can be included with the coupling member  74 . The attachment mechanism  136  includes a suction cup  166 . A center  168  of the suction cup  166  is coupled with a member  170  extending through an opening  172  in the coupling member  74 . The member  170  is movably coupled with a cam  174  included on an actuation lever  176 . 
     In operation, the coupling member  74  is positioned so the suction cup  166  is in contact with the writing surface  28 . Pressure is applied to the suction cup  166  to force air out from between the suction cup  166  and the writing surface  28 . Forcing the air out causes a vacuum to be formed between the suction cup  166  and the writing surface  28 . As illustrated, an end of the actuation lever  176  is then actuated so as to rotate the cam  174 . The rotation of the cam  174  causes the center of the suction cup  166  to be pulled toward the coupling member  74 . The coupling member  74  can include supports  178  which keep the coupling member  74  at a constant displacement from the writing surface  28 . Since the coupling member  74  is at a constant distance from the writing surface  28 , the motion of the center  168  of the suction cup  166  toward the coupling member  74  serves to increase the amount of vacuum between the suction cup  166  and the writing surface  28 . As a result, the user actuated suction cups  166  can support a load exceeding the load which is supportable by normal suction cups. The increased load support ability provides sufficient support for a detector assembly  72  to be mounted to a vertical writing surface  28 . 
     Although the above discussion describes the user actuated attachment mechanism  136  as being included on the coupling member  74 , the attachment mechanism  136  can be included on a first and/or second detector  12 A,  12 B which stands independently or which is included in a detector assembly  72 . Further, the number of user actuated attachment mechanisms  136  on a single detector and/or coupling member  74  can be increased until a detector or detector assembly is held firmly in place on a writing surface  28 . 
     In FIG. 7D, the detectors  12 A,  12 B are illustrated as having a 180 degree angular range of reception. However, is noted that the detectors  12 A,  12 B preferably have ranges of reception selected from the group of about 70 to 110 degrees, about 80 to 100 degrees, about 90 degrees, about 160 to 200, about 170 to 190 degrees, and about 180 degrees. 
     As illustrated in FIGS. 7A and 7C, the angular range of reception can be at least partially defined by a shielding element  140 . The shielding element  140  is oriented relative to the position signal receiver  60  to shield the position signal receiver  60  from position signals transmitted by the stylus  10  when the stylus  10  is positioned outside a predetermined region  180 . FIGS. 7N and 7O illustrate portions of a predetermined region  180  for detectors  12 A,  12 B with a range of reception of about 90 degrees and about 180 degrees respectively. In FIG. 7N, the predetermined region  180  has an angular range of about 90 degrees extending outward from the detector parallel to the writing surface  28 . In FIG. 7O, the predetermined region  180  has an angular range of about 180 degrees extending outward from the detectors  12 A,  12 B parallel to the writing surface  28 . The predetermined region preferably has an angular range selected from the group including about 70 to 110 degrees, about 80 to 100 degrees, about 90 degrees, about 160 to 200, about 170 to 190 degrees, and about 180 degrees. 
     The detector assembly may include a plurality of control switches  182  and an indicator  184 , as illustrated in FIGS. 7D,  7 F and  7 O. The user can activate each control switch  182  to control various functions which are performed by the processing unit  20  or the hardware unit  14 . For example, activating a control switch can cause the current monitor image  34  to be saved; cause the current monitor image  34  to be saved and moved to the background while a new monitor image area  36  is brought to the foreground for the creation of a new monitor image  34 ; cause the current monitor image  34  to be moved to the background while a new monitor image area  36  is brought to the foreground for the creation of a new monitor image  34 ; cause a copy of the current monitor image to be saved in the background while the current monitor image remains in the foreground for any additional adjustments; cause the entire monitor image  34  to be erased while retaining the current monitor image area  36  in the foreground; bring a new monitor image area  36  into the foreground; maximize the current monitor image area  36  to fill the available space on the monitor; bring the last monitor image area  36  to the foreground when another program was last used in the foreground; notify the processing unit  20  that an overlay has been positioned on the writing surface; notify the processing unit  20  that an overlay has been removed form the writing surface; enable or disable selected functions; change or select the color of particular strokes on the monitor image  34 ; change the particular color correlated with a particular stylus  10 ; fax the monitor image  34 ; E-mail the monitor image  34 ; and/or print the monitor image  34 . As discussed, certain embodiments of the transcription system require calibration, and activating a particular control switch can initiate calibration or recalibration. As discussed, the transcription system can be used simultaneously with other programs. Activating the control switches can serve to control the various functions of these other programs. For instance, actuating a particular control switch can cause POWER POINT to move to the next slide or display. Similarly, activating a different control switch  182  can cause POWER POINT to move to the previous slide or display. A wide variety of additional system functions can be envisioned and are intended to fall within the scope of the present invention. 
     The indicators  184  can be used to indicate to the user a condition of the system. For instance, an indicator  184  can be an LED which flashes when a power source within the stylus  10  is running low in power, to acknowledge that a control switch  182  has been activated and/or to acknowledge that an error condition has occurred. 
     As illustrated in FIGS. 6A,  7 B and  7 C, the first and/or the second detector  12 A,  12 B can include a contact switch  186  coupled with the detector electronics  130 . The contact switch is closed when the detectors  12 A,  12 B is positioned adjacent the writing surface  28  and is opened when the detectors  12 A,  12 B are removed from the writing surface  28 . The detector electronics can include logic for identifying when the contact switch has gone from closed to open. In response, the detector electronics  130  can provide a re-calibrate signal which is received by the hardware unit  14 . The hardware unit  14  includes logic for identifying the re-calibrate unit. 
     Electronics 
     FIG. 8A illustrates a block diagram for controlling the transmission and emission of the various reference signals  64  and position signals  66  and for determining the time for the first and second detectors  12 A,  12 B to receive a position signal  66 . Various portions of block diagram are positioned in the first detector  12 A, the second detector  12 B, the hardware unit  14 , the processing unit  20  and/or an implement  210  which can be either a stylus  10  or an eraser  16 . For instance, the implement  210  includes a reference signal receiver  56  coupled with a trigger circuit  188  which is coupled with a position signal transmitter  58 . The trigger circuit  188  triggers the transmission of a position signal  66  in response to receiving a reference signal  64 . The first detector  12 A includes a position signal receiver  60  coupled with a first detector circuit  190 . The second detector  12 B includes a reference signal transmitter  62  and a position signal receiver  60  coupled with a second detector circuit  192 . The detector circuits provide a signal when the position signal receiver  60  has received a position signal  66 . 
     The output from the first detector circuit stops a first timer  194  and asserts a first toggle within a toggle block  196 . The output from the second detector circuit  192  stops a second timer  198  and asserts a second toggle within the toggle block  196 . The first timer  194 , the second timer  198  and the toggle block  196  can be located within the hardware unit  14  and/or the processing unit  20 . 
     The hardware unit  14  and/or the processing unit  20  includes a hardware controller  200 . Examples of hardware controllers that can be used include, but are not limited to microsequencer, microcontroller or microprocessor. The hardware controller  200  periodically provides a DRV_XMIT signal on a DRV_XMIT line. The DRV_XMIT signal is received by the first timer  194 , the second timer  198 , the toggle block  196  and the reference signal transmitter  62  in the second detector  12 B. The DRV_XMIT signal is also received by a timeout counter  202 . 
     In operation, the hardware controller  200  provides a DRV_XMIT signal which causes the reference signal transmitter  62  to transmit a reference signal  64 , resets the first and second timers  194 ,  198  and clears any toggles within the toggle block  196  which were previously asserted. The reference signal receiver  56  receives the reference signal  64 . The trigger circuit  188  triggers the position signal transmitter  58  to transmit a position signal  66 . The position signal receiver  60  within the first detector  12 A receives the position signal  66  and the first detector circuit provides a signal indicating that a position signal  66  has been received. The signal from the first detector circuit stops the first timer  194  and asserts the first toggle in the toggle block  196 . The position signal receiver  60  in the second detector  12 B receives the position signal  66  and the second detector circuit  192  provides a signal indicating that a position signal  66  has been received. The signal from the second detector circuit  192  stops the second timer  198  and asserts the second toggle in the toggle block  196 . 
     When the first and second toggles are asserted, an RCV_DONE? signal is received by the hardware controller  200 . The hardware controller  200  sequentially activates the tri-state buffers  204 . The data from the first timer  194  is received on a bus  206  via the tri-state buffers  204 . The data from the second timer  198  is received on the bus  206  via the tri-state buffers  204 . The processing unit  20  can receive information from the bus  206  via a UART  208 . After the data from the first timer  194  and the second timer  198  is received on the bus  206 , the DRV_XMIT signal is provided again. 
     When the time out counter reaches some pre-determined limit, called the timeout limit, before both toggles in the toggle block  196  are asserted, the DRV_XMIT signal is provided without the data on the first and second timers being received by the bus  206 . As a result, if one of the detectors  12 A,  12 B misses a position signal  66 , the next cycle of position detection is performed. The timeout limit can be administratively set to some value which is appropriate for most writing surfaces  28 . The timeout limit can also be calculated by the processing unit  20  or the hardware controller  200 . When the timeout limit is calculated, the timeout limit can be determined by dividing the writing area diagonal, D, by the speed of sound. The calculated timeout can be increased by some administratively determined factor. Whether the timeout limit is an administratively set value or a calculated value, it is conceivable that the transcription system can record the position of the implement when the implement is positioned outside the writing area  38  or off the writing surface  28 . 
     FIG. 8B illustrates another embodiment of a block diagram for controlling the transmission and emission of the various reference signals  64  and position signals  66 . The block diagram is suitable for use with the system illustrated in FIG.  2 C. The implement  210  includes a reference signal transmitter  62  and the hardware unit  14  includes a reference signal receiver  56 . The trigger circuit  188  in the implement  210  is designed so a reference signal  64  and a position signal  66  are regularly transmitted from the implement  210  with a period on the order of a typical administratively set timeout limit. 
     In operation, the reference signal  64  is received by the reference signal receiver  56 . Receipt of the reference signal  64  causes the first timer  194  and the second timer  198  to be cleared. The position signal  66  is received by the first and second detectors  12 A,  12 B, stopping the first and second timers  194 ,  198  and asserting the first and second toggles within the toggle block  196 . When the first and second toggles are asserted, an RCV_DONE? signal is received by the hardware controller  200 . The hardware controller  200  sequentially activates the tri-state buffers  204  to deliver the data from the first and second timers  194 ,  198  to the bus  206 . Since the reference signal  64  and the position signal  66  are periodically transmitted, the above sequence is repeated when the hardware unit  14  receives another reference signal  64  from the implement  210 . 
     FIG. 8C illustrates another embodiment of a block diagram which can be used with the system illustrated in FIG.  2 C. The implement  210  includes a reference signal transmitter  62  and the hardware unit  14  includes a reference signal receiver  56 . The trigger circuit  188  in the implement  210  is designed so for each reference signal  64  transmitted from the implement  210 , a plurality of position signals  66  are regularly transmitted from the implement  210  with a period on the order of the timeout limit. 
     In operation, upon activation of the implement electronics by placing the implement  210  in contact with the writing area  38 , a reference signal  64  is transmitted from the implement  210  along with a position signal  66 . The reference signal  64  is received by the reference signal receiver  56 . In response to receiving the reference signal  64 , the hardware controller  200  provides an DRV_XMIT signal which clears the first timer  194 , the second timer  198  and the timeout counter  202 . The position signal  66  is received by the position signal receivers  60 , stopping the first and second timers  194 ,  198  and asserting the first and second toggles within the toggle block  196 . When the first and second toggles are asserted, an RCV_DONE? signal is received by the hardware controller  200 . The hardware controller  200  sequentially activates the tri-state buffers  204  to deliver the data from the first and second timers  194 ,  198  to the bus  206  and over a serial communication line via the UART  208  to the processing unit  20 . 
     After the timeout counter reaches a defined time interval, the hardware controller  200  provides another DRV-XMIT signal. The defined time interval is equal to the period which the position signals  66  are transmitted from the implement  210 . This time interval allows the hardware controller  200  to provide DRV-XMIT signals with the same frequency that the position signals  66  are transmitted. Further, the DRV-XMIT signals are provided at approximately the same time the position signals  66  are transmitted. As a result, the reference signal  64  serves to synchronize the DRV-XMIT signals with the transmission of position signals  66 . The reference signal  64  can be transmitted with a frequency which is sufficient to prevent drift in the synchronization between the transmission of the position signals and the DRV-XMIT signals. 
     In each of FIGS. 8A-8C, the hardware unit  14  includes control switches  182 . Signals from the control switches  182  and the position signal receiver  60  are received by the hardware controller  200 . Suitable control switches  182  include, but are not limited to toggle switches and contact switches. Each hardware unit  14  also includes indicators  184  which can be activated by the hardware controller  200  or the processing unit. The indicators can be used to indicate to the user various conditions of the system. Suitable indicators include, but are not limited to, an LED, an LCD display, an LED display, a speaker for providing audible messages, a beeper and a buzzer. 
     In operation, the control switches  182  can be activated by the user. Based on the particular control switch  182  which is activated, the hardware controller  200  can perform a particular function itself or can load a second control signal onto the bus  206 . The processing unit  20  can include logic for identifying the second control signal and carrying out a function in response to the particular control signal. Examples of functions which can be carried out by the hardware unit  14  or the processing unit are described above. 
     The hardware controller  200  can include logic for identifying various signals encoded into the position signals or encoded into the reference signals. For instance, the hardware controller  200  can include logic which identifies a power signal, an identity signal and/or a pressure signal encoded into position signals  66  or reference signals. In response to identifying at least one of these signals, the hardware controller  200  can load a second power, identity and/or pressure signal onto the bus  206 . The second power, identity and pressure signals can be the same or different than the power, identity and pressure signals which were originally received. The hardware controller  200  can also activate an indicator  184  in response to identifying one of these signals. For instance, the indicator can be an LED and the hardware controller  200  can light the LED in response to identifying a power signal. As discussed above, the hardware controller  200  can include logic for identifying the implement  210  based on the response of the implement  210  to an inquiry signal. When the implement  210  has been identified, an identity signal can be loaded onto the bus  206 . The processing unit  20  is in communication with the bus  206  and can include logic for identifying and responding to at least one of the signals which have been loaded onto the bus  206 . The response of the processing unit  20  to identifying these signals will be discussed in more detail below. 
     The hardware controller  200  can also include logic for identifying error conditions. Example error conditions include, but are not limited to, a user&#39;s hand blocking a portion of the position signal transmitter and a detector  12 A,  12 B being moved after the system was calibrated. These error conditions can be identified when one of the detectors  12 A,  12 B receives a position signal while the other detector does not. The error condition can be identified when an RCV_DONE? signal is not received before the next cycle is begun as indicated by transmission of a position signal. The lack of the RCV_DONE? signal indicates that only one or none of the toggles were asserted before a new cycle was initiated as indicated by transmission of a position signal. When this condition is met for some pre-determined number of cycles, an error condition has occurred. The user can be notified of this indication via an indicator  184 . For instance, the indicator can be an LED which flashes when the error condition is identified or a speaker which produces an audible message or an audible beep. Further, the hardware unit  14  can load an error signal onto the bus so it can be received by the processing unit. The processing unit can include logic for identifying the error signal and responding to it. For instance, upon identifying the error signal, the processing unit can cause an error message to appear on the monitor. 
     The hardware controller  200  illustrated in FIGS. 8A-8C can include logic for identifying when the implement  210  has been removed from the writing area  38 . For instance, when position signals are not received for some pre-determined period of time, the implement can be characterized as being removed. One method for determining that the predetermined period of time is elapsed is to monitor the number of times that the timeout counter  202  consecutively reaches the timeout limit. When a pre-determined number of timeouts has been achieved, the implement  210  is characterized as being removed from the writing area  38 . The number of timeouts that should occur before the implement  210  is characterized as removed from the writing area  38  is preferably 1-20, more preferably 2-10 and most preferably 2-3. 
     The hardware controller  200  can also include logic for communicating to the processing unit  20  that the implement  210  has been removed from the writing area  38 . As illustrated in FIGS. 8A-8C, signals from the hardware controller  200  can be received by the bus  206 . When the hardware controller  200  identifies that the implement  210  has been removed from the writing area  38 , the hardware controller  200  can load a stylus removed signal onto the bus  206 . The processing unit  20  includes logic for identifying the stylus removed signal and adjusting the monitor image  34  accordingly. 
     The hardware controller  200  can also be coupled with detector circuits  190 ,  192  within the first or second detector  12 A,  12 B. The hardware controller  200  can include logic for identifying a re-calibrate signal provided by the detector electronics. As described above, the recalibrate signal occurs when the first or second detector  12 A,  12 B has been removed from the writing surface  28 . In response to identifying the re-calibrate signal, the hardware controller  200  can load a second re-calibrate signal onto the bus where it can be accessed by the processing unit. In response, the processing unit can initiate a re-calibration of the system. 
     The hardware controller  200  can also include logic for encoding inquiry signals into the reference signals  64  transmitted from the reference signal transmitter  62 . As described in more detail below, these inquiry signals are identified by the implement  210  which can respond to the inquiry signal. The sequence of inquiry signals and responses can be used to identify the implement  210 . 
     In each of FIGS. 8A-8C, the hardware controller  200  is coupled with a temperature sensor  212  so as to receive a temperature signal from the temperature sensor  212 . There is a known relationship between the speed of sound and temperature. As will be described in detail below, the speed of sound can play a role in calibration of the transcription system and determining the position of the stylus  10 . As a result, the hardware controller  200  can produce a second temperature signal which is received by the processing unit  20 . The processing unit  20  can process the second temperature signal to determine the speed of sound which can then used in calibration and position calculations. The processing unit  20  can also include logic for monitoring the second temperature signal and periodically recalculating the speed of sound. Alternatively, the hardware controller  200  can include logic for processing the temperature signal to determine the speed of sound. The hardware controller  200  can then produce a speed of sound signal which is received by the processing unit  20 . The processing unit  20  can then process the speed of sound signal to determine the speed of sound for use in calculations. The hardware controller can also include logic for periodically monitoring the temperature sensor  212  and updating the speed of sound signal. 
     Although the temperature sensor  212  is illustrated as being located within the hardware unit  14 , the temperature sensor is preferably located where it can be positioned close to the writing surface  28  during operation of the transcription system. Proximity to the writing surface  28  provides information regarding the temperature at the writing surface  28  where changes in the temperature are most likely to influence the transcription system. Suitable locations for the temperature sensor  212  include, but are not limited to, a first detector  12 A, second detector  12 B, or coupling member  74 . The temperature sensor  212  can also be included in an independent module which can be coupled to the writing surface  28 . Further, the temperature sensor  212  can be coupled directly to the processing unit  20 . As a result, the processing unit  20  can receive and process the temperature signal directly. Additionally, the transcription system can include a plurality of temperature sensors  212  in different locations to maximize the accuracy of temperature determinations or to identify the existence of temperature gradients. Suitable temperature sensors  212  include, but are not limited to, thermocouples and thermistors. 
     The hardware units  14  illustrated in FIGS. 8A-8C can include an internal power source such as a battery or can include a cable to an external power source such as a wall socket or the processing unit  20 . The hardware units  14  can also include a power switch, such as a toggle switch, for turning the hardware unit  14  on and/or off. One of the indicators  184  can indicate whether the hardware unit  14  is on or off. For instance, the indicator  184  can be an LED which is lit when the hardware unit  14  is switched in. Further, the hardware unit  14  can include a power level sensor for detecting a level of power available to the hardware unit  14 . When the available power level falls below a particular threshold level, this can be indicated to the user by an indicator  184 . For instance, the indicator  184  can be an LED which is lit when the power level falls below the threshold or an LED used to indicate whether the hardware unit  14  is on or off can flash when the power level falls below a particular threshold. 
     The block diagrams illustrated in FIG. 8A-8C can be readily adapted for use with other transcription system embodiments, such as the transcription system embodiments illustrated in FIGS. 2B-2D. For example, in order to adapt the block diagrams for use with the transcription system illustrated in FIG. 2B, the reference signal transmitter  62  and the reference signal receiver  56  can be replaced with a wire for carrying the reference signal  64 . 
     In FIGS. 8A-8C, the first and second detector circuits  190 ,  192  are illustrated as being positioned in the first and second detectors  12 A,  12 B. It is noted, however, that the first and second detector circuits  190 ,  192  may also be included in the hardware unit  14 . Further, the reference signal transmitter  62  is illustrated as being positioned in the second detector  12 B in FIGS. 8A and 6B. However, the reference signal transmitter  62  can also be positioned in other locations within the system including the hardware unit  14 . Further, although the hardware unit is illustrated as a housing containing electronics, the hardware unit can refer to a collection of electronics which perform the functions discussed as being performed within the hardware unit. As a result, the hardware unit is conceivably distributed among several locations. 
     The block diagrams illustrated in FIGS. 8A-8C can be adapted for use with other systems. For instance, the block diagram illustrated in FIG. 8A can be adapted for use with the system illustrated in FIG. 3B by including a reference signal receiver  56  within the first detector  12 A and replacing the position signal receiver  60  in the first detector  12 A with a position signals transceiver  70 . The first detector  12 A can then be designed so the position signal transceiver  70  responds to receiving a reference signal  64  during calibration of the system by transmitting a position signal  66 . 
     An example of a trigger circuit  188  that may be included in the implement electronics  104  is illustrated in FIG.  9 . The trigger circuit  188  triggers the position signal transmitter  58  to transmit a position signal  66  in response to a reference signal receiver  56  receiving a reference signal  64 . The circuit can be included in the stylus  10  or in the eraser  16 . The trigger circuit  188  includes a transistor  214 , a first node  220 , a second node  222  and a transformer  224 . An n-channel MOSFET transistor is shown with a self-contained zener diode, but other suitable devices might also be used. A power source  226  is coupled with the first node  220 . Suitable power sources  226  include, but are not limited to, a battery such as a 5 V battery. Suitable position signal transmitters include, but are not limited to, an ultrasound transducer. 
     The first node  220  is also coupled with the transformer. A suitable transformer transforms the 5 V signal to a 570 V peak-to-peak signal. The transformer  224  is coupled with the source of the transistor  214 . The drain of the transistor is coupled with the ground. The transformer  224  is coupled with the ultrasound transducer  58 . A resistor  216  is coupled in parallel between the transformer to assist in damping electrical ringing. When the potential at the second node  222  exceeds a threshold potential, current flows from the power source  226 , through the transformer  224  and the transistor  214 , to the ground. The voltage output from the transformer  224  drives the ultrasound transducer  58 . As a result of this configuration, the ultrasound position signal  66  is triggered by the IR reference signal  64 . 
     As shown above, the second node  222  is coupled with the base of the transistor  214 . The second node  222  can also be coupled with additional electronics within the implement electronics  104  and/or a reference signal detector via an amplifier (not shown). The second node  222  can also be coupled with the hardware unit  14  via an electrical wire  68  as illustrated in FIG.  2 B. When the second node  222  is coupled with the hardware unit  14 , the ultrasound position signal  66  is triggered by a reference signal  64  received via the electrical wire  68 . Similarly, when the second node  222  is coupled with a reference signal receiver, the ultrasound position signal  66  is triggered by a reference signal  64  received at the reference signal receiver. 
     FIG. 10 illustrates a detector circuit which may be used as the first and/or second detector circuit illustrated in FIGS. 8A-8C. The detector circuit is typically included in the detector electronics  130  but may be positioned in another location within the system. The detector circuit includes an amplifier  230 , a low pass filter  232 , rectifier  234  and a comparator  236 . In operation, the signal received at the position signal receiver  60  is amplified and then filtered. The filtered signal is then rectified. The rectified signal is provided to the comparator which provides a signal when the signal from the rectifier rises above some threshold value. The signal from the comparator indicates that a position signal  66  has been received at the position signal receiver  60 . 
     In the circuit illustrated in FIG. 10, the presence of the rectifier  234  improves the quality of the monitor image  34 . One source of error in creation of the monitor image  34  results when the leading edge of the position signal  66  does not exceed the comparator&#39;s  236  threshold value but a subsequent part of the same signal does exceed the threshold value. This error results in the stylus  10  appearing further from first and second detectors  12 A,  12 B than the true location of the stylus  10 . Rectifying the signal increases the opportunity for the comparator&#39;s threshold value to be exceeded and the position signal  66  detected. The earlier a position signal  66  is detected, the less severe the error described above. As a result, the rectifier  234  serves to reduce the error resulting from missed position signals  66 . 
     Converting Time of Flight Signals to a Recorded Image 
     FIGS. 11A-11B illustrate how the time of flight measurements may be translated into an image on a monitor image area  36 . The first and second detectors  12 A,  12 B are displaced by a distance, L. The writing area  38  has a width dimension, W, a height dimension, H and a diagonal direction, D. Similarly, the monitor image area  36 , has a width dimension, w and a height dimension h. Each of these dimensions are illustrated in FIG.  11 A. The L, H and W dimensions can be known values or can be determined during calibration of the system. Once, the H and W dimensions are determined, the monitor image area  36  is created on the monitor  22 . The monitor image area  36  is created with a h:w ratio which matches the ratio of H:W. As a result, the actual h and w values can vary. After the monitor image area  36  is created, the size and dimensions of the monitor image area  36  can be adjusted by the user using traditional techniques for manipulating windows. For instance, a mouse can be used to click and drag an edge or corner of the monitor image area  36 . Further, the size of the monitor image  34  relative to the monitor image area  36  can be magnified and reduced by the user with traditional techniques for magnifying and reducing images on a monitor. An example of a typical techniques for user magnification and reduction of images and image areas is used in drawing programs such as VISIO, etc.. Scroll bars can be included on the monitor image area  36  to scroll to portions of the monitor image  34  which are not currently displayed on the monitor. It is conceivable that the user may write outside the writing area  38 . When a user writes outside the writing area, the processing unit can include logic for expanding the size of the monitor image area  36  to accommodate positions outside the writing area  38 . 
     As illustrated in FIG. 11B, a Cartesian coordinate system can be transposed on the writing area  38 . The coordinate system is transposed on the writing area  38  so the corners of the writing area  38  is positioned at (0, 0), (0, H), (W, 0) and (W, H). The position of the stylus  10  relative to the corners of the writing area  38 , (x, y), can be determined using Equation 1 and Equation 2.              x   =         L   2     -     r   2     +     l   2         2      L               Equation 1               y   =       (       l   2     -     x   2       )       1   /   2               Equation 2                         
     As illustrated in FIG. 11B, the variable l represents the distance between the stylus  10  and the first detector  12 A. The variable r represents the distance between the stylus  10  and the second detector  12 B. The variables r and l can be calculated from Equation 3 and Equation 4. 
     
       
           I=Ct   1   Equation 3  
       
     
     
       
           r=Ct   2   Equation 4 
       
     
     The variable t 1  is the time of flight of the position signal  66  between the stylus  10  and the first detector  12 A and t 2  is the time of flight of the position signal  66  between the stylus  10  and the second detector  12 B. C is the speed of sound. As described above, C can be a function of temperature. As described above, the transcription system can include a temperature sensor  212  and logic for determining the speed of sound from temperature measurements. As a result, when the transcription system includes a temperature sensor  212 , the determined speed of sound is used in these calculations. When the transcription system does not include a temperature sensor  212 , the speed of sound at standard conditions can be used.              y   =         L   2     +     l   2     -     r   2         2      L               Equation 5               x   =       (       r   2     -     y   2       )       1   /   2               Equation 6                         
     FIG. 11C illustrates the first and second detectors  12 A,  12 B positioned along a side of the writing area  38 . The Cartesian coordinate system transposed on the writing area  38  illustrated in FIG. 11B is transposed on the writing area  38  illustrated in FIG.  11 C. Although the coordinate system is the same, the changed position of the first and second detectors  12 A,  12 B relative to writing area  38  requires a different set of equations to determine the stylus position, (x, y). The stylus position, (x, y), can be determined using Equation 5 and Equation 6. 
     As illustrated in FIGS. 11B and 11C, a Cartesian coordinate system is also transposed on the monitor image area  36 . The corners of the monitor image area  36  are defined as (0, 0), (0, H), (W, 0) and (W, H) so they are correlated to the position of the writing area corners  38 . As a result, the stylus position, (x, y), on the writing area  38  translates to a position on the monitor image area  36 . 
     Creation of the monitor image  34  is illustrated in FIG.  11 D. The stylus position, (x, y) is periodically sampled as the stylus is moved along the writing area  38 . For instance, during the stroke illustrated in FIG. 11C, the stylus position during each sample is expressed as a set of Cartesian coordinates, (x n , y n ). The sampled positions are then translated to positions on the monitor image area  36 . The image forms when line segments are drawn between consecutively sampled positions which have been translated to the monitor. The resolution of the monitor image  34  can be increased by increasing the frequency that the stylus position, (x, y), is sampled. Further, the resolution of the monitor image  34  can also be smoothed with position filtering logic as will be discussed below. 
     Data Structures 
     FIG. 12 provides a block diagram of an embodiment of the system. The processing unit  20  illustrated includes a processor  238  in communication with a memory  240  including a volatile memory  242  and a storage unit  244 . Suitable processing units  20  include, but are not limited to, IBM and Macintosh personal computers and central servers. The processor  238  is also in communication with the hardware unit  14  via an input/output unit  246  and a serial channel  248 . Suitable processors  238  include, but are not limited to, microprocessors and CPUs. The storage unit can include logic and various data structures. The volatile memory  242  is utilized during execution of the logic included in the storage unit  244 . 
     FIG. 13 illustrates a data structure for an image data structure which can be stored in the memory  240 . The image data structure includes a column of x fields  250  correlated with y fields  252 . As described above, the position of the stylus  10  relative to the detectors is periodically sampled as the stylus  10  is moved along the writing area  38 . The Cartesian coordinates for the sampled positions are stored in the image data structure. The x coordinate for each sampled position is stored in an x field and the y coordinate for the position is stored in the corresponding y field. 
     The monitor image  34  is created by forming lines between sequential positions in the image data structure to form a stroke. Certain rows can include break entries which indicate that the stylus  10  was removed from the writing surface  28 . These entries are created when an activation or deactivation signal  66  has been received as discussed above. When such an entry exists, lines, splines and the like may be drawn between the series of positions following the entry but not between positions on opposite sides of the entries. As a result, a second stroke is created which is independent of the first stroke. 
     FIG. 14 illustrates an implement characteristic data structure  254  which can be stored in the memory  240 . The implement characteristic data structure  254  includes a column of implement identifier fields  256  correlated with implement fields  258 , first implement characteristic fields  260  and second implement characteristic fields  262 . The implement identifier field  256  lists an identifier which can be unique to each type of implement which can be used on the writing area  38 . For instance, each type of stylus  10  and each type of eraser  16  can be identified by a unique number. Each implement field  258  lists whether the implement is an eraser  16 , a stylus  10  or other implement which can be used on the writing area  38 . The first implement characteristic field  260  and the second implement characteristic field  262  list characteristics of the implement identified in the corresponding implement field  258 . For instance, when the identified implement is a stylus  10 , the first implement characteristic field  260  can list information indicating the color or thickness of the stroke left by the stylus  10 . The implement characteristic data structure  254  can optionally include additional implement characteristic fields which can list additional implement characteristics. 
     The implement characteristic data structure  254  is used to identify the implement being used on the writing area  38 . As a result, when the eraser  16  is being used on the writing area  38 , the monitor image  34  is erased. Further when the stylus  10  is being used on the writing area  38 , the characteristics correlated with the identified stylus  10  can be used to create each stroke on the monitor image  34 . For instance, when a blue stylus  10  is used to write on the writing area  38 , the strokes which appears on the monitor image  34  can be created with a blue color. As a result, the characteristics of the monitor image  34  can be reflected in the written image  44 . 
     It is noted that the system can be adjusted such that when strokes of different colors cross over each other, the system may either display one stroke on top of the other stroke, or illustrate the overlapping portion of the strokes as a mixture of the different colors. For example, when a blue stroke is written over a yellow stroke, the system may either record the overlapping portion as being the first stroke (yellow), the last stroke (blue), or a combination of the two strokes (green). By providing a mixture of the different colored strokes, the actual appearance of the image formed by the different strokes can be better simulated. 
     FIG. 15A illustrates an control section relative to template data structure which can be stored in the memory  240 . The control section relative to template data structure includes a function field  264  and a plurality of coordinate fields  266 - 280 . The plurality of coordinate fields include an x′ upper left corner field  266 , a y′ upper left corner field  268 , an x′ upper right corner field  270 , a y′ upper right corner field  272 , an x′ lower left corner field  274 , a y′ lower left corner field  276 , an x′ lower right corner field  278  and a y′ lower right corner field  280 . The x′ upper left corner field  266  and the y′ upper left corner field  268  lists the coordinates of the upper left corner of a particular control section  32  on the template  18 . Similarly, the remaining coordinate fields  270 - 280  list the coordinates for other corner of the particular control section  32 . The coordinates are listed relative to the template  18 . For instance, an imaginary or real coordinate system can be transposed on the template  18  with the origin of the coordinate system located at one calibration mark  40  and an axis of the coordinate system extending through another calibration mark  40 . The coordinates listed in fields  266 - 280  are measured on the transposed coordinate system. As a result, the listed coordinates indicate the spatial relationship of each control section  32  relative to the calibration marks  40 . 
     Each set of coordinate fields  266 - 280  is correlated with a function field  264  which lists a function performed by the hardware unit  14  or the processing unit  20  when the stylus  10  is positioned within the control section  32  defined by the coordinate fields  266 - 280 . For instance, when the stylus is positioned within an control section  32  with coordinates corresponding to the function field  264  labeled “print”, the hardware unit  14  or the processing unit  20  will cause the monitor image  34  to be printed. Similarly, when the stylus is positioned within an control section  32  with coordinates corresponding to the function field  264  labeled “2”, the hardware unit  14  or the processing unit  20  will cause the number 2 to be displayed in the display  48  of the calculator image  46 . 
     FIG. 15B illustrates an control section relative to detectors data structure which can be stored in the memory  240 . The control section relative to detectors data structure includes function fields  264  similar to the function fields listed in the control section relative to template data structure. The control section relative to detectors data structure also includes a plurality of coordinate fields  282 - 296 . The plurality of coordinate fields  282 - 296  include an x upper left corner field  282 , a y upper left corner field  284 , an x upper right corner field  286 , a y upper right corner field  288 , an x lower left corner field  290 , a y lower left corner field  292 , an x lower right corner field  294  and a y lower right corner field  296 . The x upper left corner field  282  and the y upper left corner field  284  respectively list the x and y coordinates of the upper left corner of a particular control section  32  on the template  18 . Similarly, the remaining fields  286 - 296  list the coordinates for other corners of the control section  32 . The coordinates are listed relative to the detectors  12 A,  12 B. Specifically, the coordinates listed in fields  282 - 296  are measured on a coordinate system such as the coordinate systems illustrated in FIG.  11 B and/or FIG.  11 C. As a result, the listed coordinates indicate the spatial relationship of each control section  32  relative to the detectors  12 A,  12 B. 
     The data structures illustrated in FIGS. 15A and 15B presume control sections  32  which are rectangular in shape, however, it is contemplated that control sections  32  with alternative shapes are also suitable for use with the template  18 . For instance, the control sections  32  can be circular, triangular, elliptical, etc.. A single template  18  can include control sections  32  with a single control section  32  geometries or with different geometries. When the template  18  includes circular control sections  32 , the data structures illustrated in FIG. 15A and 15B can include fields which contain information defining the position of the center of the circles and fields which contain information defining the diameter of the circles. Similarly, when the template  18  includes triangular control sections  32 , the data structures illustrated in FIG. 15A and 15B can include fields which contain information defining the positions of each of the three corners of the triangles. 
     Process Flows 
     The transcription system can optionally include calibration logic, stylus identification logic, image creation logic and overlay calibration logic. The transcription system can also optionally include handwriting recognition logic for converting the monitor image  34  directly into ASCII text or converted directly into presentation software such as Microsoft Power Point. Any of the logic discussed above or below can be included on a computer readable medium which can be loaded onto the processing unit  20  or the hardware controller  200  The logic may also be stored remotely and loaded onto a local processor unit or the hard ware unit by electronic transmission over a public network, such as the INTERNET. Suitable computer readable media include, but are not limited to, computer disks, floppy disks, compact disks, tapes such as magnetic tapes, personal digital assistants, hand held computers. Similarly, the logic can be remotely stored and accessed via a network or modem. 
     The calibration logic guides the user in calibrating the system and can determine variables required for operation of a particular embodiment of the transcription system. For instance, the calibration logic can include logic for determining a displacement between detectors, a displacement between calibration marks and the detectors, a displacement between a template and the detectors, and a displacement between a control section and the detectors, and the writing area dimensions. As will be described in more detail below, the logic required can vary between different embodiments of the transcription system. 
     The calibration logic may be accessed when the user installs the transcription system on a new writing surface. The calibration logic can also be accessed at the command of the user when the user feels the system may have become uncalibrated. The re-calibrate command can be given by activating a particular control switch  182 , by positioning the stylus within the perimeter of a particular control on the template, section or by using a user interface to provide particular input to the processing unit or hardware unit. Further, the calibration logic can be broken up into smaller bits of logic which can be accessed independently as will be described below. 
     An example of calibration logic process flow is illustrated in FIG.  16 A. Portions of the calibration logic which pertain to logic for determining the detector displacement, the control section positions and the writing area dimensions are labeled as such in the brackets along the left edge of FIG.  16 A. The process flow of FIG. 16A is suitable for use with the systems illustrated in FIGS. 2A-2D which can require use of the template  18  during the determination of the displacement between the detectors. Because the template is used during the determination of the displacement between the detectors  12 A,  12 B and during determination of the control section positions, there can be some overlap in the logic used to determine the control section positions and in the logic used to determine the detector displacement. This overlap is illustrated by labeled brackets which vertically overlap in FIG.  16 A. 
     The logic for determining the writing area dimensions can be independent from the logic for determining detector displacement and control section position as illustrated by the brackets in FIG.  16 A. As a result, it is conceivable that different portions of the calibration logic can be accessed independently, i.e. at different times during operation of the transcription system. For instance, the user can determine control section positions several times but determine the writing area dimensions once but As a result, the user can move the template  18  to a new position on a writing surface and then determine the new control section positions without having to re-determine the dimensions of the writing area. 
     In FIG. 16A, control is passed from the start block  298  to process block  300 . At process block  300  the user is directed to touch the stylus  10  to the calibration mark  40  in the upper left corner of the template  18 . The direction takes the form of creating a template image  42  on the monitor  22  and showing a stylus  10  contacting the upper left corner of the template  18  as discussed with respect to FIG.  1 C. Control is then passed to process block  302  where the time for the position signal  66  to pass from the stylus  10  to the first detector  12 A and the second detector  12 B, t 1  and t 2 , is accessed from the bus  206 . Control is then passed to process block  304  where r and l are calculated via Equation 3 and Equation 4. The calculated r and l are stored as r 1  and l 1 . Control is then passed to process block  306  where the user is directed to touch the stylus  10  to the calibration mark  40  in the upper right corner of the template  18 . Control is then passed to process block  308  where the time for the position signal  66  to pass from the stylus  10  to the first detector  12 A and the second detector  12 B, t 1  and t 2 , is accessed from the bus  206 . Control is then passed to process block  310  where r and l are calculated via Equation 3 and Equation 4. The calculated r and l are then stored as r 2  and l 2 .              L   =       (       (       l   2   2     -     l   1   2       )     -     (       r   2   2     -     r   1   2       )       )       2        W   T                 Equation 7                         
     Control is passed from process block  310  to process block  312  where the displacement between the detectors, L, is determined by using the stored r 1 , l 1 , r 2 , and l 2  in Equation 7, where w T  is a known constant equal to the width between the calibration marks  40  on the template  18 . The calculated L is then stored. 
     Control is passed from process block  312  to process block  314  where the coordinates of the control sections  32  on the template  18  is determined relative to the detectors  12 A,  12 B. L, r 1 , l 1 , r 2  and l 2  are used in Equation 1 and Equation 2 to determine and store the coordinates of the calibration marks  40  relative to detectors  12 A,  12 B. As discussed above, the control section relative to template data structure lists the coordinates of the control sections  32  relative to the calibration marks  40  on the template  18 . Using traditional principles of geometry, these coordinates can be used in combination with the determined positions of the calibration marks  40  relative to the detectors, to determine the coordinates for the control sections  32  relative to the detectors  12 A,  12 B. The determined coordinates for the control sections are entered into the appropriate fields of the control section relative to detectors data structure. 
     Control is passed form process block  314  to process block  316  where the user is prompted to position the stylus within a particular one of the control sections  32 . The prompt can take the form of the prompts discussed above with respect to process blocks  300  and  306 . Control is then passed to decision block  318  where a determination is made whether the position of the control sections relative to the detectors has been properly calculated. The determination can be made by calculating r and l for when the stylus is positioned within the perimeter of the particular control section at process block  316 . The determined r and l are used in Equations 1 and 2 to determine the position of the stylus  10  relative to the detectors. The determined position is checked against the fields of the control section relative to detectors data structure which correspond the particular control section to determine whether the determined position falls within the particular control section. When the determined position does not fall within the perimeter of the particular control section, the determination is negative and control is passes to process block  320 . At process block  320  the user is provided with an error message indicating an error during the calibration. For example, the error message can be a readable massage shown on the monitor or an indicator on the hardware unit can be activated to indicate the error condition. Control is returned from process block  320  to process block  300 . 
     When the determination at decision block  318  is positive, control is passed to process block  322  where the dimensions of the writing area  38 , W and H, are determined using one of several techniques. For instance, the user can be presented with a menu of typical writing area dimensions on the monitor  22  and the user can then use a user interface  24  to select the appropriate writing area dimensions from the menu. Additionally, the user can use a user interface  24  to directly enter the dimensions of the writing area  38  into the processing unit. In another technique where the first and second detectors  12 A,  12 B define the writing area  38  and the template is positioned along a bottom edge of the writing area as illustrated in FIG. 11B, W can be set equal to the stored L. To determine H, the L, r 1  and r 2  determined as described above are used in Equations 1 and 2 to determine y 1  for the upper left calibration mark  40 . The determined y 1  is then used in Equation 8 to determine the writing area height, H, where C is a constant equal to about the height of the template  18 . Equations 7 and 8 are appropriate for use with the transcription system illustrated in FIG. 11B but can be easily adapted to the transcription system of FIG. 11C using the principles of triangulation. Once the writing area dimensions are determined by any of the above techniques, W and H are stored along with the calculated L. 
     Control is passed from process block  322  to process block  324  where the writing 
     
       
           D =( H   2   +W   2 ) ½   Equation 9 
       
     
     area diagonal  38  is determined via Equation 9 and stored. The timeout limit is then determined by dividing the length of the diagonal, D, by the speed of sound. The timeout limit can be stored and/or loaded onto the bus  206  where it can be accessed by the hardware controller  200 . 
     Control is passed from process block  324  to process block  326 . The ratio of W:H is then calculated and used to define a monitor image area  36  as illustrated in FIG.  1 D. The monitor image area  36  is the position on the monitor  22  where the monitor image  34  will be formed. The ratio of the length and width of the monitor image area  36 , h:w, is equal to the ratio of W:H. Control is then passed to the exit block  328 . 
     As described above, certain embodiments of the transcription system do not require that the timeout limit be calculated such as when the timeout limit is an administratively determined value. As a result, the need to determine the timeout limit as described with respect to process block  324  can be eliminated. Further, if the user does not intend to use the control sections  32  on the template, the need to perform the functions in process blocks  314 - 421  can be eliminated. As a result, the logic illustrated in FIG. 16A is intended to be illustrative and must be adjusted to accommodate different embodiments of the transcription system. 
     The calibration logic illustrated in FIG. 16A can be easily adapted for use with other transcription systems. For instance, FIG. 16B illustrates calibration logic which is similar to the logic illustrated in FIG. 16A, however, process block  312  is moved to a position between the start block  298  and the process block  300 . Such calibration logic is suitable for use with the systems of FIGS. 3B-3E. 
     In the systems of FIG. 3B-3E, the determination of the displacement between the detectors  12 A,  12 B can be independent of the template  18 . As a result, the logic for determining the displacement of the detectors, position of the control sections and dimensions of the writing area can be independent of one another as illustrated by the brackets along the left edge of FIG.  16 B. As a result, in certain embodiments of the transcription system, the user can determine the writing area dimensions and detector displacement once but determine the detector displacement or the control section positions several times. As a result, a user can move the template  18  to a new position on the writing surface and determine the new control section positions without having to re-determine the dimensions of the writing area or re-determine the detector displacement. 
     The logic used to determine the displacement between the detectors  12 A,  12 B in the systems of FIGS. 3B-3E can vary depending on which system is used. To determine the detector displacement with the system of FIG. 3C, the user is prompted to position the stylus  10  at the calibration mark  40  on the first detector  12 A and the time for the position signal  66  to travel from the first detector  12 A to the second detector, t 2 , is determined. The displacement between the detectors, L, is then determined by multiplying t 2  by the speed of sound. The dimension L can then stored in the memory and control passed to process block  300  of FIG.  16 B. 
     To determine the displacement between the detectors in the system of FIG. 3B, the processing unit  20  or hardware unit  14  can cause the reference signal receiver  56  and the position signal transceiver  70  on the first detector  12 A to become engaged. The processing unit  20  or hardware unit  14  can also cause a reference signal  64  to be transmitted from the second detector  12 B. The reference signal  64  will be received at the reference signal receiver  56 . In response, a position signal  66  is transmitted from the position signal transceiver  70  and the time for the position signal to travel between the first and second detectors, t 2  is determined. The displacement between the detectors, L, is then determined by multiplying t 2  by the speed of sound. The dimension L can then stored in the memory and control passed to process block  300  of FIG.  16 B. 
     As described above, certain embodiments of the transcription system do not require that the timeout limit be calculated. As a result, the need to perform the acts described with respect to process block  324  is eliminated. Further, the template is not required for calibration of the transcription systems illustrated in FIGS. 3B and 3C and can be eliminated from the transcription system. As a result, the need to perform the determine control section position logic can also be eliminated. Consequently, it is conceivable to calibrate the transcription systems illustrated in FIGS. 3B and 3C by performing only the acts described with respect to process blocks  312 ,  322 , and  326  of FIG.  16 B. 
     It is not necessary to determine the displacement between the detectors in the system of FIGS. 3D and 3E because the coupling member  74  can keep the detectors  12 A,  12 B at a known displacement. As a result, the determine detector displacement logic can be eliminated from FIG. 1 6 B. Additionally, when the timeout limit does not need to be calculated, the need to perform the functions in process blocks  324  is eliminated. Further, the need to perform the determine control section position logic can be eliminated by removing the template  18  from the system. As a result, it the transcription systems of FIGS. 3D and 3E can be operated by performing only the acts described with respect to process block  322  and  326 . 
     The above calibration logic process flows are intended to be exemplary and are not intended to limit the calibration techniques. For instance, many techniques for determining the writing area dimension as discussed with respect to process block  322  are conceivable but not disclosed. Further, various combinations of the techniques disclosed with respect to process block  322  can also be used to determine the writing area dimensions. 
     The writing area  38  dimensions calculated during the above calibration logic can be stored in the memory  240  for subsequent uses. As a result, the system does not need to be calibrated each time the system is used. Each time the system is turned on, the user can be asked if the system has been positioned on a new writing surface  28 . This inquiry can take the form of a question on the monitor  22 . When the user indicates that the system has not been positioned on a new writing surface  28 , the processing unit  20  can work from the previously stored writing area  38  dimensions. In other embodiments, the system can depend on the user to calibrate the system when the system is positioned on a new writing surface  28 . In these embodiments, the system does not need to inquire whether the system has been positioned on a new writing surface  28 . In other embodiments, the bus is monitored for a re-calibrate signal which is placed on the bus by the hardware unit  14  when the first or second detector  12 A,  12 B has been removed from the writing surface  28 . When a re-calibrate signal is identified, the system must be re-calibrated once the system is re-installed on another writing surface  28 . As a result, one of the above calibration logic process flows can be accessed when the re-calibrate signal is detected. 
     A process flow of the image creation logic is illustrated in FIG.  17 . Control is passed from the start block  330  to decision block  334  where a determination is made whether a stylus  10  or eraser  16  is being used in the writing area  38 . This determination can be made by monitoring the bus  206  for signals which are a result of output from a stylus  10  or an eraser  16 . When the determination is negative, control is returned to decision block  334 . When the determination is positive, control is passed to process block  336  where the implement is identified by monitoring the bus  206  for an identity signal. Control is then passed to decision block  338  where a determination is made whether the implement is an eraser  16 . This determination is made by accessing the implement characteristic data structure  254 . The implement identity signal is compared with the implement identifier fields  256  until a match is found. The corresponding implement field  258  is accessed to identify whether the implement is a stylus  10  or an eraser  16 . When the determination is positive, control is passed to subroutine  340  where the portion of the written image  44  which is erased is also erased from the monitor image  34 . Control is then returned to decision block  334 . 
     When the determination at decision block  338  is negative, control is passed to decision block  342  where the first implement characteristic field  260  and the second implement characteristic field  262  corresponding to the identified stylus  10  are accessed. The first and second characteristics of the stylus  10  stored in the memory  240 . Control is then passed to process block  344  where t 1  and t 2  are received. Control is then passed to process block  346  where t 1  and t 2  are used in Equations 1 and 2 or 5 and 6, depending on the system being used, to determine the stylus position, (x, y). 
     Control is passed from process block  346  to decision block  348 . At decision block  348 , a determination is made whether the stylus position, (x, y), is within any of the control sections  32  of the template  18 . The determination can be made by comparing the (x, y) with the coordinates sets listed in the control section relative to detectors data structure. When the determination is negative, control is passed from decision block  348  to process block  350  where the current stylus position, (x, y), is stored in the image data structure. 
     Control is passed from process block  350  to process block  352  where the image data structure is filtered. For instance, in one filtering technique the position which was most recently stored in the image data structure is compared with a moving average of positions stored before the most recently stored position. If the most recently entered position deviates from the moving average by more than a threshold deviation, the most recently entered position can be rejected by removing it from the image data structure. The number of positions that should be included in the moving average is preferably 2-100, more preferably 2-20 and most preferably 4-10. Another filtering technique includes determining the distance of the most recently entered position from the previously entered position. When the distance is above some threshold displacement, the most recently entered position can be rejected by removing it from the image data structure. 
     The filtering techniques described above can eliminate two sources of error which can arise during use of the system. One source of error derives from reflections of positions signals  66 . During a position detection cycle, a position signal  66  can be reflected off an object such as the user and then interfere with the next detection cycle. Another source of error can result from sudden variations in the system. For instance, the stylus  10  can suddenly be held at a different angle to the writing surface  28 . These sources of error can be eliminated by using either of the filtering techniques disclosed above alone or in combination. 
     After filtering at process block  352 , control is passed to process block  354  where the image data structure is compressed. A single line can be represented as only two positions. As a result, redundant positions along a line can be eliminated to reduce the number of positions necessary to create the monitor image  34 . The compression can take the form of fitting the series of positions to a more compact form such as a spline. 
     Control is passed from process block  354  to process block  356  where the monitor image  34  is updated by plotting the most recent entry in the image data structure on the monitor image  34  and creating a line between the most recent entry in the image data structure and the previous entry in the image data structure. The line is created using the first and second implement characteristic of the stylus  10  which were determined at decision block  342 . 
     When the determination at decision block  348  is positive, control is passed to process block  358 . At process block  358 , the function listed in the function field correlated with the control section  32  where the stylus  10  is positioned is performed. For instance, a new monitor image area  36  may be created on the monitor  22  so a new monitor image  34  can be created or the previous monitor image  34  may be saved. 
     Control is passed from process block  356  and process block  358  to decision block  360 . At decision block  360 , a determination is made whether the stylus  10  is still on the writing area  38 . This determination can be made by monitoring the bus  206  for signals which are a result of output from a stylus  10 . When a pre-determined period of time passes without detecting such a signal, the determination is negative, however, when such signals are received within the pre-determined period of time, the determination is positive. In another embodiment the determination can be made by monitoring the bus  206  for a stylus removed signal loaded onto the bus  206  by the hardware controller  200 . When a stylus removed signal is detected, the determination is negative and when a stylus removed signal is not detected, the determination is positive. In other embodiments, the determination can be made using a combination of these two techniques. When the determination is positive, control is returned to process block  344 . When the determination is negative, control is passed to process block  362  where a break entry is placed in the image data structure. Control is then returned to decision block  334 . 
     The pressure placed on the stylus  10  can also be taken into account during the above process flow. As described above, the hardware controller  200  can load onto the bus  206  a pressure signal which indicates the pressure being placed on the stylus  10  by the user. The processing unit  20  can receive the pressure signal and can include logic for adjusting the width of strokes on the monitor  22  in response to the amount of pressure being placed on the stylus  10 . For instance, when a line width is listed in a first or second implement characteristic field  260 ,  262 , the listed line width can be increased or decreased in proportion to the pressure being placed on the stylus  10 . When line widths are not listed in the first or second implement characteristic fields  260 ,  262 , a standard line width can be used for each stylus  10 . The standard line width can be adjusted according to the amount of pressure being placed on the stylus  10 . 
     FIG. 18 illustrates a process flow for an image erasing subroutine. Control is passed from the start block  366  to process block  368  where the time for the position signal  66  to pass from the stylus  10  to the first detector  12 A and the second detector  12 B, t 1  and t 2 , is received. Control is then passed to process block  370  where t 1  and t 2  are used in Equations 1 and 2 or 5 and 6, depending on the system being used, to determine the position of the eraser  16  (x, y). Control is then passed to process block  372  where positions listed on the image data structure which fall within the approximate eraser area  124  are identified. The identification can be made by using a relationship between the approximate eraser area  124  and the position of the eraser  16 . For instance, when the eraser  16  has a round shape, the approximate eraser area  124  can be defined to cover all points within two inches of the eraser  16  position. All the positions listed in the image data structure which are within two inches of the eraser  16  position are then identified. 
     Control is passed from process block  372  to process block  374  where the identified positions are removed from the image data structure. Control is then passed to process block  376  where the monitor image  34  is updated. The image update can take the form of removing from the monitor image  34  the positions which are removed from the image data structure or re-creating the monitor image  34 . Control is then passed to decision block  378  where a determination is made whether the eraser  16  is still positioned on the writing area  38 . This determination can be made by monitoring the bus  206  for signals which are a result of output from the eraser  16 . When a pre-determined period of time passes without detecting such a signal, the determination is negative, however, when such signals are received within the pre-determined period of time, the determination is positive. In another embodiment the determination can be made by monitoring the bus  206  for an stylus removed signal loaded onto the bus  206  by the hardware controller  200 . When an stylus removed signal is detected, the determination is negative and when an eraser removed signal is not detected, the determination is positive. In other embodiments, the determination can be made using a combination of these two techniques. When the determination is positive, control is returned to process block  368 . When the determination is negative, control is passed to the return block  379  which returns control to the image creation logic. 
     The processing unit  20  can also include logic which allows the creation of the monitor image  34  to be played back to the user. This is possible when the monitor image  34  is stored in an image data base as opposed to being stored as a bitmap. During the playback, the monitor image  34  is created by sequentially plotting and connecting the positions listed in the image data structure on the monitor image area  36 . The process of plotting and connecting positions is performed at a rate which allows the user to observe the image creation. The playback of the monitor image  34  allows the user to re-capture information which has been erased or can extract information from the actual creation of the monitor image  34 . Further, the user can stop the playback at a particular point and edit the image at the point where it was stopped. 
     As discussed above, several different embodiments of the system can identify the type of implement being used upon the writing area  38 . For instance, whether the implement is an eraser  16  or a stylus  10  can be identified as well as the type of the eraser  16  or stylus  10 . Different types of styluses  10  can write with different colors or line widths. Different types of erasers  16  can be erasers  16  have a footprint with a different size or shape. Different types of implements are generally listed in the implement characteristic data structure  254  with different implement identifiers. 
     FIGS. 19A-19B illustrate one embodiment of implement identification logic. The implement identification logic operates via a series of inquiries and responses between the implement and the hardware controller  200  or the processing unit  20 . The implement responds to the inquiries by responding or not responding to the inquiry signals with a position signal  66 . The implement identification process flow can be accessed each time the implement produces an activation signal. As a result, the implement is identified each time the implement contacts the writing area  38 . 
     The process flow illustrated in FIG. 19A can be included in the hardware controller  200  of the hardware unit  14 . The process flow can also be adapted for inclusion in the processing unit  20 . Control is passed from the start block  380  to process block  382 . At process block  382 , an inquiry signal is transmitted to the implement. The inquiry signal can be coded into a reference signal  64 . The implement electronics  104  includes logic which receives the reference signal  64  and recognizes the inquiry signal. The logic interprets the inquiry signal as inquiring whether the implement is the same type of implement which was last used on the writing area  38 . 
     Control is passed from process block  382  to decision block  384  where a determination is made whether the implement is a type which matches the type requested by transmission of the inquiry signal. The determination is based on whether the implement responds to the inquiry signal by transmitting a position signal  66 . When the implement responds with a position signal  66 , the determination is positive and when the implement does not respond, the determination is negative. 
     When the determination at decision block  384  is negative, control is passed from decision block  384  to process block  386  where an inquiry signal is transmitted to the implement. The implement includes logic which recognizes the signal as inquiring whether the implement is a particular type of implement. Control is then passed to decision block  388  where a determination is made whether the implement is a type which matches the type requested by transmission of the inquiry signal. The determination is based on whether the implement responds to the inquiry signal by transmitting a position signal  66 . When the implement responds with a position signal  66 , the determination is negative and when the implement does not respond, the determination is positive. When the determination is positive, control is passed to process block  390  where the t 1  and t 2  values for the transmitted position signal  66  are loaded onto the bus 206. Control is then returned to process block  386 . 
     When the determination at decision block  384  is positive, control is passed to process block  392  where the t 1  and t 2  values for the transmitted position signal  66  are loaded onto the bus  206 . Control is passed from process block  392  to process block  394 . Similarly, when the determination at decision block  388  is positive control is passed to process block  394 . At process block  394 , an identity signal is loaded onto the bus  206 . The processing unit  20  can use the identity signal to match the implement being used with a implement listed in an implement identifier field  256  of the implement characteristic data structure  254 . As a result, the processing unit  20  can identify the implement being used on the writing area  38 . Control is passed from process block  394  to exit block  396 . 
     FIG. 19B illustrates a process flow which is included in the implement electronics  104  and which is complementary to the process flow illustrated in FIG.  19 A. Control is passed from start block  398  to process block  400  where an inquiry signal is received. The inquiry signal can be coded in a reference signal  64  from a reference signal transmitter  62 . The implement electronics  104  can include logic for identifying the inquiry signal. The logic also interprets the inquiry as an inquiry whether the implement is a particular type of implement. Control is passed from process block  400  to decision block  402  where a determination is made whether the implement is the type of implement inquired about in the inquiry signal. When the determination is negative control is returned to decision block  404 . 
     At decision block  404  a determination is made whether the received inquiry signal is the first inquiry signal the implement has received during the period of time the implement has been continuously in contact with the writing area  38 . When the determination is negative, control is passed to process block  406  where the implement transmits a position signal  66 . Control is then returned to process block  400 . Similarly, when the determination at decision block  404  is positive, control is passed to process block  400 . 
     When the determination at decision block  402  is positive, control is passed to decision block  408 . At decision block  408  a determination is made whether the received inquiry signal is the first inquiry signal the implement has received during the period of time the implement has been continuously in contact with the writing area  38 . When the determination is positive, control is passed to process block  410  where the implement transmits a position signal  66 . Control is passed from process block  410  to exit block  412 . Similarly, when the determination at decision block  408  is negative, control is passed to exit block  412 . 
     The above implement identification logic can include additional logic for prioritizing transmission of the inquiry signals. For instance, the inquiry signals can be transmitted so the inquiries pertaining to the most recently used implement types are transmitted at the beginning of a series of inquiries. Further, inquiry signals relating to the least recently used or unused implement types can be transmitted later in the inquiry sequence. For instance, if a red stylus  10  is used first, an eraser  16  second and a black stylus  10  third, the next series of inquiry signals may inquire whether the stylus  10  is a black stylus  10  first, an eraser  16  second and a red stylus  10  third. Because the most recently used implements are most likely to be used for a new stroke, the prioritization scheme minimizes the number of inquiries which must be made to identify the implement. Other priority logic may also be utilized, e.g., always putting the eraser second after the last pen used. 
     The above implement identification logic also minimizes the number of position data points which are lost because the implement does not transit a position signal  66 . The first time a implement receives an inquiry signal, the implement does not respond with a position signal  66  if the implement does not match the implement sought by the inquiry signal. However, each subsequent time the implement receives an inquiry signal, the implement transmits a position signal  66  when the implement does not match the implement sought by the inquiry but does not transmit a position signal  66  when the implement does match the implement sought by the inquiry signal. As a result, a large number of non-matching inquiry signals can be transmitted and a maximum of only two data points will be lost in the process of identifying the implement. 
     The transcription system can also include calibration logic for calibrating the position of a background image relative to a writing surface. The background image may be positioned adjacent the writing surface (e.g., positioned on or behind the writing surface), may form the writing surface, or may be projected onto the writing surface. FIG. 20 illustrates an example process flow for background image calibration logic. The start block  414  is accessed when the processing unit  20  or the hardware unit  14  is notified that a background image  50  will be used with the transcription system. The user can notify the system that a background image  50  is being used by positioning the stylus tip in a particular one of the control sections  32  on the template  18  or by entering information to the processing unit  20  via the user interface  24 . Alternatively, the hardware unit  14  can include a control switch  182  which can be activated to indicate that a background image  50  is being used. 
     Control is passed from start block  414  to process block  416  where the user identifies the background image  50  which will be used in combination with the writing surface  28 . As described above, the composite images  52  can be created internally or externally and then stored in the processing unit  20  as an Image file. Upon saving composite images  52  as Image files, the user can provide each Image file with different identifying characteristics such as different names and/or different locations (i.e. different directories) within the processing unit  20 . The different identifying characteristics can be created using traditional file management programs such as WINDOWS 95, PC DOCS and IMANAGE. At process block  416 , the user can be presented with a menu listing each of the composite images  52  which has been stored as an Image file or listing each of the Image files in the current directory. The user can scroll through the list to identify the Image file of interest. Once the proper Image file has been identified, the user can select the proper Image file. One suitable method for selecting the proper Image file is using a user interface  24  which controls a cursor, such as a mouse, and double clicking on the identified Image file. Alternatively, the user can select the identified Image file by highlighting the identified Image file and then clicking on a box which may include a word such as “OK”. 
     Control is passed from process block  416  to process block  418  where the user is directed to position the background image  50  upon the writing surface  28 . The method for directing the user can be similar to the methods of directing the user to position the stylus in contact with the calibration marks  40 . Once the background image  50  is positioned relative to the writing surface  28 , the user can notify the processing unit  20  using techniques which are similar to the techniques used to notify the processing unit  20  that an background image  50  will be used. Control is passed from process block  418  to process block  420  where the user is prompted to contact the stylus tip with a calibration mark  40  present on the background image  50 . Prompting the user to contact the stylus with the calibration marks  40  on the background image  50  can be similar to the prompts discussed with respect to FIG.  1 B. For instance, the monitor image  34  can include an image of the stylus contacting the calibration point on the composite image  52 . Control is passed to process block  422  where t 1  and t 2  are determined and used in Equations 1-4 to determine the position of the first calibration mark relative to the detectors, (x 1 , y 1 ). Control is passed to process block  424  where the user is directed to contact the stylus tip with a second calibration mark  40  present on the background image  50 . Control is passed to process block  426  where t 1  and t 2  are determined and used in Equations 1-4 to determine the position of the second calibration mark  40  relative to the detectors, (x 2 , y 2 ). 
     Control is passed from process block  426  to process block  428  where the composite image  52  is created upon the monitor  22 . The composite image  52  is scaled so the first calibration mark  40  on the composite image  52  is positioned on the monitor image at (x 1 , y 1 ) and the second calibration mark  40  on the composite image  52  is positioned on the monitor image  34  at (x 2 , y 2 ). Control is passed from process block  428  to exit block  430  which can be a return to the start block of the image creation logic. 
     The logic illustrated in FIG. 20 is intended to be illustrative and not intended to be limiting. For instance, as discussed above, the background image  50  can include more than two calibration marks  40  to increase the quality of correlation between the position of the background image  50  on the writing surface  28  and the position of the background image  50  on the image area  36 . Increasing the number of calibration marks  40  can increase the number of acts required to perform out the background image calibration. 
     Additional permutations of the background image calibration logic are also contemplated. For instance, the select background image act illustrated in process block  416  can be replaced with a select background image sequence act. As discussed above a background image sequence can be a sequence of composite images  52  which are established by the user. The user can then advance through the background image sequence to the desired composite image  52 . Suitable means for advancing through the overlay image sequence include, but are not limited to, positioning the stylus tip in a particular one of the control sections  32  on the template  18 , entering information via a user interface  24  or activating a control switch  182  on the hardware unit  14 . Similar mechanisms can be used to reverse through the background image sequence. Further, when a background image is projected onto the writing surface  28 , the projector can be coupled with the processing unit  20  and the background images can be advanced or reversed with the composite images  52 . 
     The transcription system disclosed above is described with a hardware unit  14  which is independent of the processing unit  20 . It is noted, however, that the hardware unit  14  and the processing unit  20  can be integrated in a single unit. For instance, the hardware controller  200 , the processor  238 , the volatile memory  242  and the storage unit  244  can be contained in a single hardware unit  14 . The hardware controller  200  and the processor can be integrated into a single processing element. Further, the storage unit  244  and/or the volatile memory can be incorporated into a single memory device. Integrating the hardware unit  14  and the processing unit  20  permits the functions which are characterized above as performed by the processing unit  20  to performed by the hardware unit  14 . For instance, the image data structure can be created and stored within the hardware unit  14  as the written image  34  is created. As a result, the monitor image  34  can be stored without using a processing unit  20  and without being displayed on a monitor  22 . After the image data structure has been stored in the hardware unit  14 , the hardware unit  14  can be coupled with a monitor  22 , a printer, a network and/or a processing unit  20 . These connections respectively allow the image stored in the hardware unit  14  to be displayed, printed, forwarded to another location or downloaded to another storage medium. 
     Additionally, while the hardware unit  14  is illustrated above as a housing for a plurality of electronics, it is noted that the hardware unit  14  can refer to any collection of electronics which perform the function(s) of the electronics within the illustrated hardware unit. As a result, the hardware unit can actually be distributed among different locations throughout a transcription system. Further, the hardware unit can be included in several different housings and/or several different types of housings. 
     Further, the first and second detectors  12 A,  12 B are disclosed as being removable from a writing surface  28 . However, the first and second detectors  12 A,  12 B can also be integrated with the writing surface  28 . In embodiments where the first and second detector  12 A,  12 B are integrated with the writing surface  28 , the calibration acts described above can be eliminated since the writing area  38  dimensions will be constants which can be administratively entered into the system before the system is sold to the end consumer. Additionally, although the system is disclosed with first and second detectors  12 A,  12 B, additional detectors may be added to the system to facilitate the calibration process, to provide additional resolution to the monitor image  34  or the further refine the monitor image  34 . 
     EXAMPLE 
     The following is an example of a transcription system according to the present invention, its contents and operation. FIG. 21 illustrates a transcription system kit. As illustrated, the kit includes a detector assembly  512 , a set of styli  514 , a set of whiteboard markers  516 , an eraser  518 , and a template  520 . 
     FIG. 22 illustrates a stylus  514  which has been taken apart so that a marker  516  can be placed within the stylus  514 . As illustrated, the stylus  514  includes a stylus body  522  which houses a AAA battery  524  and an ultrasound transmitter  526  adjacent a writing end  528  of the stylus. The stylus  514  also includes a side cover  530  which is sufficiently clear or translucent such that one can see the marker  516  through the side cover  530 . The stylus  514  also includes a cap  532  which is sufficiently clear or translucent such that one can see a writing tip of the marker  516  through the cap  532 . 
     FIGS. 23A and 23B illustrate a stylus  514  containing a marker  516 . FIG. 23A illustrates a side view of the stylus  514  where the stylus cover  530  is in full view. As illustrated, the writing tip  538  of the marker is uncapped and the cap  532  is attached to an end  536  of the stylus  514  opposite the writing end  528 . As can be seen in FIG. 23A, the marker  516  is in full view within the stylus  514  through the stylus cover  530 . 
     FIG. 23B illustrates a side view of the stylus  514  where the stylus cover  530  is on top and the stylus body  522  is below. As illustrated, the writing tip  538  of the marker  516  is capped by the cap  532 . The cap  532  preferably seals the writing tip to prevent the marker  516  from drying out. As can be seen, the cap  532  is sufficiently clear or translucent such that one can see the writing tip  538  of the marker through the cap  532 . This allows the user to rapidly identify the color of the marker. 
     FIG. 24A illustrates the detector assembly  512  unfolded (folded in FIG.  21 ). The detector assembly includes two signal receivers  534 A,  534 B, two suction cup assemblies with attachment levers  536 A,  536 B and a series of user inputs  538 A-E. 
     FIG. 24B illustrates the detector assembly  512  attached to a whiteboard surface via the suction cup assemblies. 
     FIG. 24C illustrates the user inputs  538 A-E on the detector assembly  512 . The new board input causes the transcription system software to save what has been inputted on the whiteboard and to open a new blank file for capturing transcription information. The bookmark board input causes the transcription system software to save what has been inputted on the whiteboard while retaining the currently displayed information. The print board input causes what is currently being electronically displayed by the transcription system to be printed. The maximize board input causes the transcription system application window to be maximized and make the transcription system application the active window. The locate template input causes the transcription system software to activate the run a protocol to determine the position of the template on the whiteboard. 
     FIG. 25 illustrates how the detector assembly  512  can be attached to a processor via a connection cable  540 , in this instance a processor of a personal computer. As illustrated, the detector assembly  512  includes a data port  542  to which a detector assembly connector  544  on the connection cable  540  can be attached. The connection cable  540  also includes a serial connector  546  for connecting the connection cable  540  to one of the serial ports  549  of the personal computer. As illustrated, the connection cable  540  includes a keyboard passthrough  547 . As a result, it is possible to connect the keyboard passthrough  547  to the keyboard port  548  of the personal computer and connect the keyboard  551  to the keyboard passthrough  547 . When the detector assembly  512  is connected to the personal computer, a light  553  on the detector assembly  512  goes on. 
     FIG. 26A illustrates a user interface  550  for the transcription system. As illustrated, the user interface  550  illustrates putting the detector assembly  512  in the upper left hand corner of the writing surface. FIG. 26B illustrates a whiteboard  552  with a detector assembly  512  attached and a smiley face  554  written using a transcription system stylus. FIG. 26B also illustrates the user interface  550  which shows an electronically transcribed image  556  of the smiley face  554 . 
     FIG. 27A illustrates the user interface  550  in greater detail and some of the functions which the user interface  550  performs. For example, the user interface  550  includes a board display area  558  where captured data is displayed. The user interface  550  also includes various toolbars. Three of the most common toolbars are illustrated: The main toolbar  560  includes various common Windows functions including open, delete, save and print. The display toolbar  562  allows the user to change the way the data is being viewed (zoom, multiple board view, etc.). The pen toolbar  564  allows the user to alter the user to input or edit data with virtual pens and erasers. As with most Windows applications, the menu bar  566  allows the user to access program features. Most of the functionality provided through the menu bar can be more readily accessed through the toolbars. The navigation toolbar  570  allows the user to alter various configuration options including board size and pen color. The playback toolbar  571  allows the user to take a recorded transcription session and to playback the transcription session. As illustrated, user can go to the beginning, move back, play, stop, move forward, or go to the end. The playback toolbar  571  also includes a sliding lever  573  which allows the user to move to any portion of the recorded transcription session by moving the sliding lever  573 . 
     FIG. 27B illustrates the display toolbar  562  and its operation. As illustrated, the display toolbar  562  includes a button for a multiple board view, a single board view, and a fill screen view. Also illustrated is a single board and multiple board display. The display toolbar  562  also includes a button for notes. Pressing the notes button brings up a notes window which may contain additional information about the image being displayed. 
     FIG. 27C illustrates the navigation toolbar  570  and its operation. As illustrated, the navigation toolbar  570  includes buttons for next board, previous board, zoom full, zoom in, and zoom out. FIG. 27C also illustrates a screen  572  where a box  574  has been drawn around a portion  576  of an image  578  and a screen  580  where the portion  576  of the image  578  has been enlarged to fit the screen  576 . 
     FIG. 27D illustrates the template  520  in greater detail. As illustrated, the template includes a series of user inputs, many of which also appear on the detector assembly  512 . The new board input causes the transcription system software to save what has been inputted on the whiteboard and to open a new blank file for capturing transcription information. The bookmark board input causes the transcription system software to save what has been inputted on the whiteboard while retaining the currently displayed information. The print board input causes the transcription system software to print what is currently being electronically displayed by the transcription system. The maximize board input causes the transcription system software to maximize the transcription system application and make the transcription system application the active window. 
     The template  520  also includes first and second calibration marks  584 ,  586  which the transcription system uses to determine the position of the template  520  relative to the detector assembly  512  a writing surface, as discussed in FIGS.  27 E( 2 )- 27 E( 4 ). 
     The template  520  also includes a calculator which allows the user to operate the transcription system and perform calculations at the writing surface using a stylus. 
     The template  520  also includes a mouse region  592  which serves as a virtual touch pad for the user. The user can move a stylus within the mouse region  592  and cause a cursor associated with the system to move. Thus, by moving the stylus within the mouse region  592 , the stylus can serve as a mouse for the system. 
     The template  520  also includes a graffiti region  594  which can recognize handwritten signals, such as handwritting graffiti used with the PALM PILOT. The system includes logic for utilizing the movement of the stylus within the graffiti region  594  and translating that movement into handwritten signals. 
     FIGS.  27 E( 1 )- 27 E( 4 ) illustrate the template  520  and the detector assembly  512  on a writing surface  582  [FIG.  27 E( 1 )] and a sequence of images [FIGS.  27 E( 2 - 4 )] displayed on a user interface to allow the transcription to determine the position of the template  520  relative to the detector assembly  512  on the writing surface  582 . In order to initiate this sequence, the user may press the locate template input on the detector assembly  512  [FIG.  54 C]. 
     As illustrated in FIG.  27 E( 2 ), the user is directed to contact a first calibration mark  584  on the template  520  with the stylus. Once the user contacts the first calibration mark  584  with the stylus, the user interface changes [FIG.  27 E( 3 )] and directs the user to contact a second calibration mark  586  on the template  520 . Once the user contacts the second calibration mark  586  with the stylus, the user interface changes [FIG.  27 E( 4 )] and directs the user to contact the checkmark box  588  on the template  520 . After performing this sequence, the transcription system knows the position of the template  520  relative to the detector assembly  512  and the user can employ the template  520 . 
     FIGS. 28A and 28B illustrate two windows which may be accessed by the navigation toolbar  570 . FIG. 28A illustrates a window which allows the user to configure the writing surface. FIG. 28B illustrates a window which allows the user to configure the stylus. 
     Once data has been introduced into the transcription system, the data can be exchanged with various application in many different ways. For example, a Windows clipboard can be used to export images from the transcription system into other applications. Alternatively, images can be identified, dragged and dropped into other applications. Alternatively, transcription system files can be saved in a variety of different formats and then opened by other applications. 
     The transcription system can be used locally or networked with other computers which include the transcription system operating system. For example, the transcription system operating system can support network conferencing through Microsoft&#39;s NETMEETING™ software. 
     While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than limiting sense, as it is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the appended claims.