Patent Publication Number: US-2023135526-A1

Title: Supplemental Device for Attachment to an Injection Device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. Pat. Application No. 16/513,416, filed on Jul. 16, 2019, which is a continuation of U.S. Pat. Application No. 14/418,802, filed on Jan. 30, 2015, which is a U.S. National Phase Application pursuant to 35 U.S.C. §371 of International Application No. PCT/EP2013/065961 filed on Jul. 30, 2013, which claims priority to European Patent Application No. 12179180.0 filed on Aug. 3, 2012. The entire disclosure contents of these applications are herewith incorporated by reference into the present application. 
     SEQUENCE LISTING 
     This application contains a Sequence Listing that has been submitted electronically as an XML file named “46567-0798003.XML.” The XML file, created on Jul. 19, 2022, is 69,605 bytes in size. The material in the XML file is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a supplemental device for attachment to an injection device. 
     BACKGROUND 
     A variety of diseases exists that require regular treatment by injection of a medicament. Such injection can be performed by using injection devices, which are applied either by medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses, for example once or several times per day. For instance, a pre-filled disposable insulin pen can be used as an injection device. Alternatively, a re-usable pen may be used. A re-usable pen allows replacement of an empty medicament cartridge by a new one. Either pen may come with a set of one-way needles that are replaced before each use. The insulin dose to be injected can then for instance be manually selected at the insulin pen by turning a dosage knob and observing the actual dose from a dose window or display of the insulin pen. The dose is then injected by inserting the needle into a suited skin portion and pressing an injection button of the insulin pen. To be able to monitor insulin injection, for instance to prevent false handling of the insulin pen or to keep track of the doses already applied, it is desirable to measure information related to a condition and/or use of the injection device, such as for instance information on the injected insulin type and dose. In this respect, WO 2009/024562 discloses a medical device with a value sensor. A Radio Frequency Identification (RFID) unit comprises a value sensor such as a pressure sensor and is integrated with a liquid medicament container to enable wireless pressure or other medicament relevant parameter value monitoring. The liquid medicament container is coupled with a first housing part of the medical device, which first housing part may for instance constitute a pre-filled disposable injection device. The RFID unit communicates wirelessly with a control circuit that is contained in a second housing part of the medical device that is releasably attached to the first housing part. The control circuit is adapted to process the values measured by the RFID unit, to compare it with pre-defined values and to provide an alert to the user if the measured values fall outside normal operating conditions, and to communicate data relating to the measured values to an external device for further data processing. 
     The control circuit of the medical device described in WO 2009/024562 can thus be used with a series of pre-filled disposable injection devices, but the requirement that the RFID unit with the value sensor is contained in the medicament container of the pre-filled disposable injection devices significantly increases the costs of the pre-filled disposable injection device. 
     It has been described, for instance in WO 2011/117212 to provide a supplementary device comprising a mating unit for releasably attaching the device to an injection device The device includes a camera and is configured to perform optical character recognition (OCR) on captured images visible through a dosage window of the injection pen, thereby to determine a dose of medicament that has been dialled into the injection device. 
     SUMMARY 
     A first aspect of the invention provides a supplemental device for attachment to an injection device. The supplemental device includes: a housing; an electromechanical switch arrangement having an open state and a closed state , the electromechanical switch arrangement comprising a protrusion configured to contact a surface of the injection device while the supplemental device is attached to the injection device; a dose dialled detector operable to detect a dose of medicament dialled into the attached injection device. The supplemental device further includes: a processor arrangement configured to: monitor the detected dose of medicament dialled into the attached injection device; detect a change in the state of the electromechanical switch arrangement; and change a display output of the supplemental device when a change in the state of the electromechanical switch arrangement is detected while a zero dose is dialled into the attached injection device. 
     The processor may be configured to change the display output of the supplemental device from a dose delivery display to a dispense-end display. 
     The processor may be configured to change the mode of the supplemental device from a sleep mode to an active mode when a change in the state of the electromechanical switch arrangement is detected while a zero dose is dialled into the attached injection device. 
     The processor may be configured to change the display output of the supplemental device by cycling through menu options. 
     The dose dialled detector may comprise an image capture device and an optical character recognition system. 
     A second aspect of the invention provides a system comprising a supplemental device according to the first aspect of the invention and an injection device. 
     The injection device may comprise: a housing; a corrugated dialling sleeve rotatably supported within the housing, the corrugated dialling sleeve having a plurality of axially aligned corrugations; and an injection button coupled to the corrugated dialling sleeve at a first end of the corrugated dialling sleeve, wherein the protrusion of the electromechanical switch arrangement is configured to engage the corrugated dialling sleeve. 
     The corrugated dialling sleeve may be configured to protrude from the housing of the injection device when a zero dose is dialled into the injection device. 
     Each trough forming the corrugations may terminate at the first end of the corrugated dialling sleeve with an incline. 
     Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures show: 
         FIG.  1   a    : an exploded view of an injection device; 
         FIG.  1   b    shows a perspective view of some detail of the injection device of  FIG.  1   ; 
         FIG.  2   a   : a schematic illustration of a supplementary device to be releasably attached to the injection device of  FIG.  1    according to an embodiment of the present invention; 
         FIG.  2   b   : a perspective view of a supplementary device to be releasably attached to the injection device of  FIG.  1    according to various embodiments of the present invention; 
         FIG.  2   c   : a perspective view of a supplementary device to be releasably attached to the injection device of  FIG.  1    according to other embodiments of the present invention; 
         FIGS.  3   a  and  3   b   : possible distributions of functions among devices when using a supplementary device (such as the supplementary devices of  FIGS.  2   a ,  2   b  and  2   c   ) together with an injection device; 
         FIG.  4   : a schematic view of the supplementary device of  FIG.  2   a    in a state where it is attached to the injection device of  FIG.  1   ; 
         FIG.  5   a   : a flowchart of a method used in various embodiments; 
         FIG.  5   b   : a flowchart of a further method used in various embodiments; 
         FIG.  5   c   : a flowchart of a still further method used in various embodiments; 
         FIG.  6   : a schematic illustration of a tangible storage medium  60  according to an embodiment of the present invention; and 
         FIG.  7   : an information sequence chart that illustrates an information flow between various devices according to embodiments of the invention; 
         FIGS.  8   a  and  8   b   : a state diagram and flowchart illustrating operation of the device of  FIG.  2   b    according to aspects of the invention; 
         FIGS.  9   a  and  9   b   : a state diagram and flowchart illustrating operation of the device of  FIG.  2   c    according to aspects of the invention; 
         FIG.  10   : a lateral cross-section taken through the injection device with a supplemental device attached; 
         FIG.  11   : an axial cross-section taken through the injection device with a supplemental device attached; 
         FIGS.  12   a  and  12   b   : a state diagram illustrating operation of the injection device with a supplemental device attached. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, embodiments of the present invention will be described with reference to an insulin injection device. The present invention is however not limited to such application and may equally well be deployed with injection devices that eject other medicaments, or with other types of medical devices. 
       FIG.  1    is an exploded view of an injection device  1 , which may for instance represent Sanofi’s Solostar (R) insulin injection pen. 
     The injection device  1  of  FIG.  1    is a pre-filled, disposable injection pen that comprises a housing  10  and contains an insulin container  14 , to which a needle  15  can be affixed. The needle is protected by an inner needle cap  16  and an outer needle cap  17 , which in turn can be covered by a cap  18 . An insulin dose to be ejected from injection device  1  can be selected by turning the dosage knob  12 , and the selected dose is then displayed via dosage window  13 , for instance in multiples of so-called International Units (IU), wherein one IU is the biological equivalent of about 45.5 micrograms of pure crystalline insulin (1/22 mg). An example of a selected dose displayed in dosage window  13  may for instance be 30 IUs, as shown in  FIG.  1   . It should be noted that the selected dose may equally well be displayed differently, for instance by means of an electronic display. 
     Turning the dosage knob  12  causes a mechanical click sound to provide acoustical feedback to a user. The numbers displayed in dosage window  13  are printed on a sleeve that is contained in housing  10  and mechanically interacts with a piston in insulin container  14 . When needle  15  is stuck into a skin portion of a patient, and then injection button  11  is pushed, the insulin dose displayed in display window  13  will be ejected from injection device  1 . When the needle  15  of injection device  1  remains for a certain time in the skin portion after the injection button  11  is pushed, a high percentage of the dose is actually injected into the patient’s body. Ejection of the insulin dose also causes a mechanical click sound, which is however different from the sounds produced when using dosage knob  12 . 
     Injection device  1  may be used for several injection processes until either insulin container  14  is empty or the expiration date of injection device  1  (e.g.  28  days after the first use) is reached. 
     Furthermore, before using injection device  1  for the first time, it may be necessary to perform a so-called “prime shot” to remove air from insulin container  14  and needle  15 , for instance by selecting two units of insulin and pressing injection button  11  while holding injection device  1  with the needle  15  upwards. 
     For simplicity of presentation, in the following, it will be exemplarily assumed that the ejected doses substantially correspond to the injected doses, so that, for instance when making a proposal for a dose to be injected next, this dose equals the dose that has to ejected by the injection device. Nevertheless, differences (e.g. losses) between the ejected doses and the injected doses may of course be taken into account. 
       FIG.  2   a    is a schematic illustration of an embodiment of a supplementary device  2  to be releasably attached to injection device  1  of  FIG.  1   . Supplementary device  2  comprises a housing  20  with a mating unit configured and embrace the housing  10  of injection device  1  of  FIG.  1   , so that supplementary device  2  sits tightly on housing  10  of injection device  1 , but is nevertheless removable from injection device  1 , for instance when injection device  1  is empty and has to be replaced.  FIG.  2   a    is highly schematic, and details of the physical arrangement are described below with reference to  FIG.  2   b   . 
     Supplementary device  2  contains optical and acoustical sensors for gathering information from injection device  1 . Information is displayed via display unit  21  of supplementary device  2 . The dosage window  13  of injection device  1  is obstructed by supplementary device  2  when attached to injection device  1 . 
     Supplementary device  2  further comprises three user input transducers, illustrated schematically as a button  22 . These input transducers  22  allow a user to turn on/off supplementary device  2 , to trigger actions (for instance to cause establishment of a connection to or a pairing with another device, and/or to trigger transmission of information from supplementary device  2  to another device), or to confirm something. 
       FIG.  2   b    is a schematic illustration of a second embodiment of a supplementary device  2  to be releasably attached to injection device  1  of  FIG.  1   . Supplementary device  2  comprises a housing  20  with a mating unit configured and embrace the housing  10  of injection device  1  of  FIG.  1   , so that supplementary device  2  sits tightly on housing  10  of injection device  1 , but is nevertheless removable from injection device  1 . 
     Information is displayed via display unit  21  of supplementary device  2 . The dosage window  13  of injection device  1  is obstructed by supplementary device  2  when attached to injection device  1 . 
     Supplementary device  2  further comprises three user input buttons or switches. A first button  22  is a power on/off button, via which the supplementary device  2  may for instance be turned on and off. A second button  33  is a communications button. A third button  34  is a confirm or OK button. The buttons  22 ,  33 ,  34  may be any suitable form of mechanical switch. These input buttons  22  allow a user to turn on/off supplementary device  2 , to trigger actions (for instance to cause establishment of a connection to or a pairing with another device, and/or to trigger transmission of information from supplementary device  2  to another device), or to confirm something. 
       FIG.  2   c    is a schematic illustration of a third embodiment of a supplementary device  2  to be releasably attached to injection device  1  of  FIG.  1   . Supplementary device  2  comprises a housing  20  with a mating unit configured and embrace the housing  10  of injection device  1  of  FIG.  1   , so that supplementary device  2  sits tightly on housing  10  of injection device  1 , but is nevertheless removable from injection device  1 . 
     Information is displayed via display unit  21  of the supplementary device  2 . The dosage window  13  of injection device  1  is obstructed by supplementary device  2  when attached to injection device  1 . 
     Supplementary device  2  further comprises a touch-sensitive input transducer  35 . It also comprises a single user input button or switch  22 . The button  22  is a power on/off button, via which the supplementary device  2  may for instance be turned on and off. The touch sensitive input transducer  35  can be used to trigger actions (for instance to cause establishment of a connection to or a pairing with another device, and/or to trigger transmission of information from supplementary device  2  to another device), or to confirm something. 
       FIGS.  3 A and  3   b    show possible distributions of functions among devices when using a supplementary device (such as the supplementary devices of  FIGS.  2   a  and  2   b   ) together with an injection device. 
     In constellation  4  of  FIG.  3   a   , the supplementary device  41  (such as the supplementary devices of  FIGS.  2   a  and  2   b   ) determines information from injection device  40 , and provides this information (e.g. type and/or dose of the medicament to be injected) to a blood glucose monitoring system  42  (e.g. via a wired or wireless connection). 
     Blood glucose monitoring system  42  (which may for instance be embodied as desktop computer, personal digital assistant, mobile phone, tablet computer, notebook, netbook or ultrabook) keeps a record of the injections a patient has received so far (based on the ejected doses, for instance by assuming that the ejected doses and the injected doses are the same, or by determining the injected doses based on the ejected doses, for instance be assuming that a pre-defined percentage of the ejected dose is not completely received by the patient). Blood glucose monitoring system  42  may for instance propose a type and/or dose of insulin for the next injection for this patient. This proposal may be based on information on one or more past injections received by the patient, and on a current blood glucose level, that is measured by blood glucose meter  43  and provided (e.g. via a wired or wireless connection) to blood glucose monitoring system  42 . Therein, blood glucose meter  43  may be embodied as a separate device that is configured to receive a small blood probe (for instance on a carrier material) of a patient and to determine the blood glucose level of the patient based on this blood probe. Blood glucose meter  43  may however also be a device that is at least temporarily implanted into the patient, for instance in the patient’s eye or beneath the skin. 
       FIG.  3   b    is a modified constellation  4 &#39; where the blood glucose meter  43  of  FIG.  3   a    has been included into blood glucose monitoring system  42  of  FIG.  3   a   , thus yielding the modified blood glucose monitoring system  42 &#39; of  FIG.  3   b   . The functionalities of injection device  40  and supplementary device  41  of  FIG.  3   a    are not affected by this modification. Also the functionality of blood glucose monitoring system  42  and blood glucose meter  43  combined into blood glucose monitoring system  42 &#39; are basically unchanged, apart from the fact that both are now comprised in the same device, so that external wired or wireless communication between these devices is no longer necessary. However, communication between blood glucose monitoring system  42  and blood glucose meter  43  takes place within system  42 &#39;. 
       FIG.  4    shows a schematic view of the supplementary device  2  of  FIG.  2   a    in a state where it is attached to injection device  1  of  FIG.  1   . 
     With the housing  20  of supplementary device  2 , a plurality of components are comprised. These are controlled by a processor  24 , which may for instance be a microprocessor, a Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA) or the like. Processor  24  executes program code (e.g. software or firmware) stored in a program memory  240 , and uses a main memory  241 , for instance to store intermediate results. Main memory  241  may also be used to store a logbook on performed ejections/injections. Program memory  240  may for instance be a Read-Only Memory (ROM), and main memory may for instance be a Random Access Memory (RAM). 
     In embodiments such as those shown in  FIG.  2   b   , processor  24  interacts with a first button  22 , via which supplementary device  2  may for instance be turned on and off. A second button  33  is a communications button. The second button may be used to trigger establishment of a connection to another device, or to trigger a transmission of information to another device. A third button  34  is a confirm or OK button. The third button  34  can be used to acknowledge information presented to a user of supplementary device  2 . 
     In embodiments such as those shown in  FIG.  2   c   , two of the buttons  33 ,  34  may be omitted. Instead, one or more capacitive sensors or other touch sensors are provided. 
     Processor  24  controls a display unit  21 , which is presently embodied as a Liquid Crystal Display (LCD). Display unit  21  is used to display information to a user of supplementary device  2 , for instance on present settings of injection device  1 , or on a next injection to be given. Display unit  21  may also be embodied as a touch-screen display, for instance to receive user input. 
     Processor  24  also controls an optical sensor  25 , embodied as an Optical Character Recognition (OCR) reader, that is capable of capturing images of the dosage window  13 , in which a currently selected dose is displayed (by means of numbers printed on the sleeve  19  contained in injection device  1 , which numbers are visible through the dosage window  13 ). OCR reader  25  is further capable of recognizing characters (e.g. numbers) from the captured image and to provide this information to processor  24 . Alternatively, unit  25  in supplementary device  2  may only be an optical sensor, e.g. a camera, for capturing images and providing information on the captured images to processor  24 . Then processor  24  is responsible for performing OCR on the captured images. 
     Processor  24  also controls light-sources such as light emitting diodes (LEDs)  29  to illuminate the dosage window  13 , in which a currently selected dose is displayed. A diffuser may be used in front of the light-sources, for instance a diffuser made from a piece of acrylic glass. Furthermore, the optical sensor may comprise a lens (e.g. an aspheric lens) leading to a magnification (e.g. a magnification of more than  3 :1 ). 
     Processor  24  further controls a photometer  26 , that is configured to determine an optical property of the housing  10  of injection device  1 , for example a colour or a shading. The optical property may only be present in a specific portion of housing  10 , for example a colour or colour coding of sleeve  19  or of an insulin container comprised within injection device  1 , which colour or colour coding may for instance be visible through a further window in housing  10  (and/or in sleeve  19 ). Information on this colour is then provided to processor  24 , which may then determine the type of injection device  1  or the type of insulin contained in injection device  1  (e.g. SoloStar Lantus with purple colour and SoloStar Apidra with blue colour). Alternatively, a camera unit may be used instead of photometer  26 , and an image of the housing, sleeve or insulin container may then be provided to processor  24  to determine the colour of the housing, sleeve or insulin container by means of image processing. Further, one or more light sources may be provided to improve reading of photometer  26 . The light source may provide light of a certain wavelength or spectrum to improve colour detection by photometer  26 . The light source may be arranged in such a way that unwanted reflections, for example by dosage window  13 , are avoided or reduced. In an example embodiment, instead of or in addition to photometer  26 , a camera unit may be deployed to detect a code (for instance a bar code, which may for instance be a one- or two-dimensional bar code) related to the injection device and/or the medicament contained therein. This code may for instance be located on the housing  10  or on a medicament container contained in injection device  1 , to name but a few examples. This code may for instance indicate a type of the injection device and/or the medicament, and/or further properties (for instance a expiration date). 
     Processor  24  further controls (and/or receives signals from) an acoustic sensor  27 , which is configured to sense sounds produced by injection device  1 . Such sounds may for instance occur when a dose is dialled by turning dosage knob  12  and/or when a dose is ejected/injected by pressing injection button  11 , and/or when a prime shot is performed. These actions are mechanically similar but nevertheless sound differently (this may also be the case for electronic sounds that indicate these actions). Either the acoustic sensor  27  and/or processor  24  may be configured to differentiate these different sounds, for instance to be able to safely recognize that an injection has taken place (rather than a prime shot only). 
     Processor  24  further controls an acoustical signal generator  23 , which is configured to produce acoustical signals that may for instance be related to the operating status of injection device  1 , for instance as feedback to the user. For example, an acoustical signal may be launched by acoustical signal generator  23  as a reminder for the next dose to be injected or as a warning signal, for instance in case of misuse. Acoustical signal generator may for instance be embodied as a buzzer or loudspeaker. In addition to or as an alternative to acoustical signal generator  23 , also a haptic signal generator (not shown) may be used to provide haptic feedback, for instance by means of vibration. 
     Processor  24  controls a wireless unit  28 , which is configured to transmit and/or receive information to/from another device in a wireless fashion. Such transmission may for instance be based on radio transmission or optical transmission. In some embodiments, the wireless unit  28  is a Bluetooth transceiver. Alternatively, wireless unit  28  may be substituted or complemented by a wired unit configured to transmit and/or receive information to/from another device in a wire-bound fashion, for instance via a cable or fibre connection. When data is transmitted, the units of the data (values) transferred may be explicitly or implicitly defined. For instance, in case of an insulin dose, always International Units (IU) may be used, or otherwise, the used unit may be transferred explicitly, for instance in coded form. 
     Processor  24  receives an input from a pen detection switch  30 , which is operable to detect whether the pen  1  is present, i.e. to detect whether the supplementary device  2  is coupled to the injection device  1 . 
     A battery  32  powers the processor  24  and other components by way of a power supply  31 . 
     The supplementary device  2  of  FIG.  4    is thus capable of determining information related to a condition and/or use of injection device  1 . This information is displayed on the display  21  for use by the user of the device. The information may be either processed by supplementary device  2  itself, or may at least partially be provided to another device (e.g. a blood glucose monitoring system). 
     The processor  24  constitutes a processor arrangement. The OCR reader  25  constitutes a dose dialled detector operable to detect a dose of medicament dialled. The PCR reader  25  also constitutes a dose delivery determiner for determining that a dose of medicament has been delivered. The OCR reader  25  and the processor  24  together constitute a quantity determiner for determining a quantity of medicament that has been delivered. The processor  24  provides a function of a clock configured to determine a current time. 
       FIGS.  5   a - 5   c    are flowcharts of embodiments of methods according to the present invention. These methods may for instance be performed by processor  24  of supplementary device  2  (see  FIGS.  2   b  and  4   ), but also by a processor of supplementary device  3  of  FIG.  2   b   , and may for instance be stored in program memory  240  of supplementary device  2 , which may for instance take the shape of tangible storage medium  60  of  FIG.  6   . 
       FIG.  5   a    shows method steps that are performed in scenarios as shown in  FIGS.  3   a  and  3   b   , where information read by supplementary device  41  from injection device  40  is provided to blood glucose monitoring system  42  or  42 &#39; without receiving information back from blood glucose monitoring system  42  or  42 &#39;. 
     The flowchart  500  starts for instance when the supplementary device is turned on or is otherwise activated. In a step  501 , a type of medicament, for example insulin, provided by the injection device is determined, for instance based on colour recognition or based on recognition of a code printed on injection device or a component thereof as already described above. Detection of the type of medicament may not be necessary if a patient always takes the same type of medicament and only uses an injection device with this single type of medicament. Furthermore, determination of the type of medicament may be ensured otherwise (e.g. by the key-recess pair shown in  FIG.  4    that the supplementary device is only useable with one specific injection device, which may then only provide this single type of medicament). 
     In a step  502 , a currently selected dose is determined, for instance by OCR of information shown on a dosage window of injection device as described above. This information is then displayed to a user of the injection device in a step  503 . 
     In a step  504 , it is checked if an ejection has taken place, for instance by sound recognition as described above. Therein, a prime shot may be differentiated from an actual injection (into a creature) either based on respectively different sounds produced by the injection device and/or based on the ejected dose (e.g. a small dose, for instance less than a pre-defined amount of units, e.g.  4  or  3  units, may be considered to belong to a prime shot, whereas larger doses are considered to belong to an actual injection). 
     If an ejection has taken place, the determined data, i.e. the selected dose and - if applicable - the type of medicament (e.g. insulin), is stored in the main memory  241 , from where it may later be transmitted to another device, for instance a blood glucose monitoring system. If a differentiation has been made concerning the nature of the ejection, for instance if the ejection was performed as a prime shot or as an actual injection, this information may also be stored in the main memory  241 , and possibly later transmitted. In the case of an injection having been performed, at step  505  the dose is displayed on the display  21 . Also displayed is a time since the last injection which, immediately after injection, is 0 or 1 minute. The time since last dose may be displayed intermittently. For instance, it may be displayed alternately with the name or other identification of the medicament that was injected, e.g. Apidra or Lantus. 
     If ejection was not performed at step  504 , steps  502  and  503  are repeated. 
     After display of the delivered dose and time data, the flowchart  500  terminates. 
       FIG.  5   b    shows in more detail exemplary method steps that are performed when the selected dose is determined based on the use of optical sensors only. For instance, these steps may be performed in step  502  of  FIG.  5   a   . 
     In a step  901 , a sub-image is captured by an optical sensor such as optical sensor  25  of supplementary device  2 . The captured sub-image is for instance an image of at least a part of the dosage window  13  of injection device  1 , in which a currently selected dose is displayed (e.g. by means of numbers and/or a scale printed on the sleeve  19  of injection device  1 , which is visible through the dosage window  13 ). For instance, the captured sub-image may have a low resolution and/or only show a part of the part of sleeve  19  which is visible through dosage window  13 . For instance, the captured sub- image either shows the numbers or the scale printed on the part of sleeve  19  of injection device  1  which is visible through dosage window  13 . After capturing an image, it is, for instance, further processed as follows:
     Division by a previously captured background image;   Binning of the image(s) to reduce the number of pixels for further evaluations;   Normalization of the image(s) to reduce intensity variations in the illumination;   Sheering of the image(s); and/or   Binarization of the image(s) by comparing to a fixed threshold.   

     Several or all of these steps may be omitted if applicable, for instance if a sufficiently large optical sensor (e.g. a sensor with sufficiently large pixels) is used. 
     In a step  902 , it is determined whether or not there is a change in the captured sub-image. For instance, the currently captured sub-image may be compared to the previously captured sub-image(s) in order to determine whether or not there is a change. Therein, the comparison to previously captured sub-images may be limited to the sub-image of the previously captured sub-images that was captured immediately before the current sub-image was captured and/or to the sub-images of the previously captured sub-images that were captured within a specified period of time (e.g. 0.1 seconds) before the current sub-image was captured. The comparison may be based on image analysis techniques such as pattern recognition performed on the currently captured sub-image and on the previously captured sub-image. For instance, it may be analyzed whether the pattern of the scale and/or the numbers visible through the dosage window  13  and shown in the currently captured sub-image and in the previously captured sub-image is changed. For instance, it may be searched for patterns in the image that have a certain size and/or aspect ratio and these patterns may be compared with previously saved patterns. Steps  901  and  902  may correspond to a detection of a change in the captured image. 
     If it is determined in step  902  that there is a change in the sub-image, step  901  is repeated. Otherwise in a step  903 , an image is captured by an optical sensor such as optical sensor  25  of supplementary device  2 . The captured image is for instance an image of the dosage window  13  of injection device  1 , in which a currently selected dose is displayed (e.g. by means of numbers and/or a scale printed on the sleeve  19  of injection device  1 , which is visible through the dosage window  13 ). For instance, the captured image may have a resolution being higher than the resolution of the captured sub-image. The captured image at least shows the numbers printed on the sleeve  19  of injection device  1  which are visible through the dosage window  13 . 
     In a step  904 , optical character recognition (OCR) is performed on the image captured in step  903  in order to recognize the numbers printed on the sleeve  19  of injection device  1  and visible through the dosage window  13 , because these numbers correspond to the (currently) selected dose. In accord to the recognized numbers, the selected dose is determined, for instance by setting a value representing the selected dose to the recognized numbers. 
     In a step  905 , it is determined whether or not there is a change in the determined selected dose and, optionally, whether or not the determined selected dose does not equal zero. For instance, the currently determined selected dose may be compared to the previously determined selected dose(s) in order to determine whether or not there is a change. Therein, the comparison to previously determined selected dose(s) may be limited to the previously determined selected dose(s) that were determined within a specified period of time (e.g. 3 seconds) before the current selected dose was determined. If there is no change in the determined selected dose and, optionally, the determined selected dose does not equal zero, the currently determined selected dose is returned/forwarded for further processing (e.g. to processor  24 ). 
     Thus, the selected dose is determined if the last turn of the dosage knob  12  is more than 3 seconds ago. If the dosage knob  12  is turned within or after these 3 seconds and the new position remains unchanged for more than 3 seconds, this value is taken as the determined selected dose. 
       FIG.  5   c    shows in more detail method steps that are performed when the selected dose is determined based on the use of acoustical and optical sensors. For instance, these steps may be performed in step  502  of  FIG.  5   a   . 
     In a step  1001 , a sound is captured by an acoustical sensor such as acoustical sensor  27  of supplementary device  2 . 
     In a step  1002 , it is determined whether or not the captured sound is a click sound. The captured sound may for instance be a click sound that occurs when a dose is dialled by turning dosage knob  12  of injection device  1  and/or when a dose is ejected/injected by pressing injection button  11 , and/or when a prime shot is performed. If the captured sound is not a click sound, step  1001  is repeated. Otherwise in a step  1003 , an image is captured by an optical sensor such as optical sensor  25  of supplementary device  2 . Step  1003  corresponds to step  903  of flowchart  900 . 
     In a step  1004 , an OCR is performed on the image captured in step  1003 . Step  1004  corresponds to step  904  of flowchart  900 . 
     In a step  1005 , it is determined whether or not there is a change in the determined selected dose and, optionally, whether or not the determined selected dose does not equal zero. Step  1005  corresponds to step  905  of flowchart  900 . 
     There might be a slight advantage of the acoustic approach shown in  FIG.  5   c    when it comes to power consumption of the supplementary device, because permanently capturing images or sub-images as shown in  FIG.  5   b    typically is more power consuming than listening to an acoustical sensor such as a microphone. 
       FIG.  6    is a schematic illustration of a tangible storage medium  60  (a computer program product) that comprises a computer program  61  with program code  62  according to aspects of the present invention. This program code may for instance be executed by processors contained in the supplementary device, for instance processor  24  of supplementary device  2  of  FIGS.  2   a  and  4   . For instance, storage medium  60  may represent program memory  240  of supplementary device  2  of  FIG.  4   . Storage medium  60  may be a fixed memory, or a removable memory, such as for instance a memory stick or card. 
     Finally,  FIG.  7    is an information sequence chart  7  that illustrates the flow of information between various devices (e.g. the injection device  1  and the supplementary device  2  of  FIG.  4    in a scenario as depicted in  FIGS.  3   a  or  3   b   ) according to an embodiment of the present invention. A condition and/or use of injection device  1  affects an appearance of its dosage window, sounds generated by injection device  1  and a colour of the housing. This information is transformed by sensors  25 ,  26 ,  27 ,  30  of supplementary device  2  into an OCR signal, an acoustic sensor signal and a photometer signal, respectively, which are in turn transformed into information on the dialled dose, on an injection/dialling operation and on the type of insulin by a processor  24  of supplementary device  2 , respectively. This information is then provided by supplementary device  2  to a blood glucose monitoring system  42 . Some or all of this information is displayed to a user via the display  21 . 
     As described in detail above, embodiments of the present invention allow connection of a standard injection device, in particular an insulin device, with a blood glucose monitoring system in a useful and productive way. 
     Embodiments of the present invention introduce a supplementary device to allow for this connection, assuming the blood glucose monitoring system has wireless or other communication capabilities. 
     The benefits from the connection between the blood glucose monitoring and an insulin injection device are inter alia the reduction of mistakes by the user of the injection device and a reduction of handling steps - no more manual transfer of the injected insulin unit to a blood glucose monitoring is required, in particular to a blood glucose monitoring system with functionality of providing guidance for the next dose based on the last dose injected and latest blood glucose values. 
     As described with reference to exemplary embodiments above, when a user/patient gets a new insulin pen, the user attaches the supplementary device to the pen. The supplementary device reads out the injected dose. It may also transfer it to a blood glucose monitoring system with insulin titration capabilities. For patients taking multiple insulins, the supplementary device recognizes the device structure to the insulin type and may also transmit this piece of information to the blood glucose monitoring system. 
     In example embodiments, the information shown on a display, for example LCD display  21  of  FIGS.  2   a  and  4   , may also converted to a sound signal played to a user through a speaker, for example by a text-to-speech functionality implemented by processor  24  using the acoustical signal generator  23 . Thus, a user with impaired vision may have improved access to the information of supplementary device  2 , such as a dialled dose, a recommended dose, a recommended time for administration and/or the like. 
     When using embodiments of the present invention, the user inter alia has the following advantages: 
     The user can use the most convenient disposable insulin injector. 
     The supplementary device is attachable and detachable (reusable). 
     Injected dose information may be transferred to the blood glucose monitoring system automatically (no more transfer mistakes). Improved dose guidance may result from this as the blood glucose monitoring system calculates the dose to be taken. 
     Keeping of a manual data logbook may not be needed any more. 
     Furthermore, when deploying the supplementary device proposed by the present invention, patients may also be reminded of injecting their next dose by receiving an alarm signal, for instance, after an appropriate time after a first dose of a medicament (for instance insulin or heparin) has been injected. 
     Injected dose information may be transferred to any computerized system, for instance as input for any dose calculation or any other applicable therapeutic guidance calculation, or for the creation of an alarm signal, for instance to remind the user of taking the next dose. 
     The term “drug” or “medicament”, as used herein, means a pharmaceutical formulation containing at least one pharmaceutically active compound. 
     In one embodiment, the pharmaceutically active compound has a molecular weight up to 1500 Da and/or is a peptide, a proteine, a polysaccharide, a vaccine, a DNA, a RNA, an enzyme, an antibody or a fragment thereof, a hormone or an oligonucleotide, or a mixture of the above-mentioned pharmaceutically active compound. 
     In a further embodiment, the pharmaceutically active compound is useful for the treatment and/or prophylaxis of diabetes mellitus or complications associated with diabetes mellitus such as diabetic retinopathy, thromboembolism disorders such as deep vein or pulmonary thromboembolism, acute coronary syndrome (ACS), angina, myocardial infarction, cancer, macular degeneration, inflammation, hay fever, atherosclerosis and/or rheumatoid arthritis, 
     In a further embodiment, the pharmaceutically active compound comprises at least one peptide for the treatment and/or prophylaxis of diabetes mellitus or complications associated with diabetes mellitus such as diabetic retinopathy, 
     In a further embodiment, the pharmaceutically active compound comprises at least one human insulin or a human insulin analogue or derivative, glucagon-like peptide (GLP-1) or an analogue or derivative thereof, or exendin-3 or exendin-4 or an analogue or derivative of exendin-3 or exendin-4. 
     Insulin analogues are for example Gly(A21), Arg(B31), Arg(B32) human insulin; Lys(B3), Glu(B29) human insulin; Lys(B28), Pro(B29) human insulin; Asp(B28) human insulin; human insulin, wherein proline in position B28 is replaced by Asp, Lys, Leu, Val or Ala and wherein in position B29 Lys may be replaced by Pro; Ala(B26) human insulin; Des(B28-B30) human insulin; Des(B27) human insulin and Des(B30) human insulin. 
     Insulin derivates are for example B29-N-myristoyl-des(B30) human insulin; B29-N-palmitoyl-des(B30) human insulin; B29-N-myristoyl human insulin; B29-N-palmitoyl human insulin; B28-N-myristoyl LysB28ProB29 human insulin; B28-N-palmitoyl-LysB28ProB29 human insulin; B30-N-myristoyl-ThrB29LysB30 human insulin; B30-N-palmitoyl- ThrB29LysB30 human insulin; B29-N-(N-palmitoyl-Y-glutamyl)-des(B30) human insulin; B29-N-(N-lithocholyl-Y-glutamyl)-des(B30) human insulin; B29-N-(ω-carboxyheptadecanoyl)-des(B30) human insulin and B29-N-(co-carboxyheptadecanoyl) human insulin. 
     Exendin-4 for example means Exendin-4(1-39), a peptide of the sequence H-His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2 (SEQ ID NO:1). 
     Exendin-4 derivatives are for example selected from the following list of compounds:
     H-(Lys)4-des Pro36, des Pro37 Exendin-4(1-39)-NH2 (SEQ ID NO:2),   H-(Lys)5-des Pro36, des Pro37 Exendin-4(1-39)-NH2 (SEQ ID NO:3),   des Pro36 Exendin-4(1-39) (SEQ ID NO:4),   Pro36 [Asp28] Exendin-4(1-39) (SEQ ID NO:5),   des Pro36 [IsoAsp28] Exendin-4(1-39) (SEQ ID NO:6),   des Pro36 [Met(O)14, Asp28] Exendin-4(1-39) (SEQ ID NO:7),   des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39) (SEQ ID NO:8),   des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39) (SEQ ID NO:9),   des Pro36 [Trp(O2)25, IsoAsp28] Exendin-4(1-39) (SEQ ID NO: 10),   des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39) (SEQ ID NO:11),   des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39) (SEQ ID NO:12); or   des Pro36 [Asp28] Exendin-4(1-39) (SEQ ID NO:5),   des Pro36 [IsoAsp28] Exendin-4(1-39) (SEQ ID NO:6),   des Pro36 [Met(O)14, Asp28] Exendin-4(1-39) (SEQ ID NO:7),   des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39) (SEQ ID NO:8),   des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39) (SEQ ID NO:9),   des Pro36 [Trp(O2)25, IsoAsp28] Exendin-4(1-39) (SEQ ID N0:10),   des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39) (SEQ ID NO:11),   des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39) (SEQ ID NO:12),   wherein the group -Lys6-NH2 may be bound to the C-terminus of the Exendin-4 derivative;   or an Exendin-4 derivative of the sequence   des Pro36 Exendin-4(1-39)-Lys6-NH2 (SEQ ID NO:13) (AVE0010),   H-(Lys)6-des Pro36 [Asp28] Exendin-4(1-39)-Lys6-NH2 (SEQ ID NO:14),   des Asp28 Pro36, Pro37, Pro38Exendin-4(1-39)-NH2 (SEQ ID NO:15),   H-(Lys)6-des Pro36, Pro38 [Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:16),   H-Asn-(Glu)5des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:17),   des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO.18),   H-(Lys)6-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:19),   H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:20),   H-(Lys)6-des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2 (SEQ ID NO:21),   H-des Asp28 Pro36, Pro37, Pro38 [Trp(O2)25] Exendin-4(1-39)-NH2 (SEQ ID NO:22),   H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:23),   H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:24),   des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:25),   H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:26),   H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:27),   H-(Lys)6-des Pro36 [Met(O)14, Asp28] Exendin-4(1-39)-Lys6-NH2 (SEQ ID NO:28),   des Met(O)14 Asp28 Pro36, Pro37, Pro38 Exendin-4(1-39)-NH2 (SEQ ID NO:29),   H-(Lys)6-desPro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:30),   H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:31),   des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:32),   H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:33),   H-Asn-(Glu)5 des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:34),   H-Lys6-des Pro36 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2 (SEQ ID NO:35),   H-des Asp28 Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25] Exendin-4(1-39)-NH2 (SEQ ID NO:36),   H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:37),   H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-NH2 (SEQ ID NO:38),   des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:39),   H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(S1-39)-(Lys)6-NH2 (SEQ ID NO:40),   H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2 (SEQ ID NO:41);   or a pharmaceutically acceptable salt or solvate of any one of the aforementioned Exendin-4 derivative.   

     Hormones are for example hypophysis hormones or hypothalamus hormones or regulatory active peptides and their antagonists as listed in Rote Liste, ed. 2008, Chapter 50, such as Gonadotropine (Follitropin, Lutropin, Choriongonadotropin, Menotropin), Somatropine (Somatropin), Desmopressin, Terlipressin, Gonadorelin, Triptorelin, Leuprorelin, Buserelin, Nafarelin, Goserelin. 
     A polysaccharide is for example a glucosaminoglycane, a hyaluronic acid, a heparin, a low molecular weight heparin or an ultra low molecular weight heparin or aderivative thereof, or a sulphated, e.g. a poly-sulphated form of the above-mentioned polysaccharides, and/or a pharmaceutically acceptable salt thereof. An example of a pharmaceutically acceptable salt of a poly-sulphated low molecular weight heparin is enoxaparin sodium. 
     Antibodies are globular plasma proteins ~150 kDa http://en.wikipedia.org/wiki/Dalton_%28unit%29) that are also known as immunoglobulins which share a basic structure. As they have sugar chains added to amino acid residues, they are glycoproteins. The basic functional unit of each antibody is an immunoglobulin (Ig) monomer (containing only one Ig unit); secreted antibodies can also be dimeric with two Ig units as with IgA, tetrameric with four Ig units like teleost fish IgM, or pentameric with five Ig units, like mammalian IgM. 
     The Ig monomer is a “Y”-shaped molecule that consists of four polypeptide chains; two identical heavy chains and two identical light chains connected by disulfide bonds between cysteine residues. Each heavy chain is about 440 amino acids long; each light chain is about 220 amino acids long. Heavy and light chains each contain intrachain disulfide bonds which stabilize their folding. Each chain is composed of structural domains called Ig domains. These domains contain about 70-110 amino acids and are classified into different categories (for example, variable or V, and constant or C) according to their size and function. They have a characteristic immunoglobulin fold in which two β sheets create a “sandwich” shape, held together by interactions between conserved cysteines and other charged amino acids. 
     There are five types of mammalian Ig heavy chain denoted by α, δ, ε, γ, and µ. The type of heavy chain present defines the isotype of antibody; these chains are found in IgA, IgD, IgE, IgG, and IgM antibodies, respectively. 
     Distinct heavy chains differ in size and composition; α and γ contain approximately 450 amino acids and δ approximately 500 amino acids, while µ and ε have approximately 550 amino acids. Each heavy chain has two regions, the constant region (C H ) and the variable region (V H ). In one species, the constant region is essentially identical in all antibodies of the same isotype, but differs in antibodies of different isotypes. Heavy chains γ, α and δ have a constant region composed of three tandem Ig domains, and a hinge region for added flexibility; heavy chains µ and ε have a constant region composed of four immunoglobulin domains. The variable region of the heavy chain differs in antibodies produced by different B cells, but is the same for all antibodies produced by a single B cell or B cell clone. The variable region of each heavy chain is approximately 110 amino acids long and is composed of a single Ig domain. 
     In mammals, there are two types of immunoglobulin light chain denoted by λ and κ. A light chain has two successive domains: one constant domain (CL) and one variable domain (VL). The approximate length of a light chain is 211 to 217 amino acids. Each antibody contains two light chains that are always identical; only one type of light chain, κ or λ, is present per antibody in mammals. 
     Although the general structure of all antibodies is very similar, the unique property of a given antibody is determined by the variable (V) regions, as detailed above. More specifically, variable loops, three each the light (VL) and three on the heavy (VH) chain, are responsible for binding to the antigen, i.e. for its antigen specificity. These loops are referred to as the Complementarity Determining Regions (CDRs). Because CDRs from both VH and VL domains contribute to the antigen-binding site, it is the combination of the heavy and the light chains, and not either alone, that determines the final antigen specificity. 
     An “antibody fragment” contains at least one antigen binding fragment as defined above, and exhibits essentially the same function and specificity as the complete antibody of which the fragment is derived from. Limited proteolytic digestion with papain cleaves the Ig prototype into three fragments. Two identical amino terminal fragments, each containing one entire L chain and about half an H chain, are the antigen binding fragments (Fab). The third fragment, similar in size but containing the carboxyl terminal half of both heavy chains with their interchain disulfide bond, is the crystalizable fragment (Fc). The Fc contains carbohydrates, complement-binding, and FcR-binding sites. Limited pepsin digestion yields a single F(ab&#39;)2 fragment containing both Fab pieces and the hinge region, including the H-H interchain disulfide bond. F(ab&#39;)2 is divalent for antigen binding. The disulfide bond of F(ab′)2 may be cleaved in order to obtain Fab&#39;. Moreover, the variable regions of the heavy and light chains can be fused together to form a single chain variable fragment (scFv). 
     Pharmaceutically acceptable salts are for example acid addition salts and basic salts. Acid addition salts are e.g. HCl or HBr salts. Basic salts are e.g. salts having a cation selected from alkali or alkaline, e.g. Na+, or K+, or Ca2+, or an ammonium ion N+(R1)(R2)(R3)(R4), wherein R1 to R4 independently of each other mean: hydrogen, an optionally substituted C1-C6-alkyl group, an optionally substituted C2-C6-alkenyl group, an optionally substituted C6-C10-aryl group, or an optionally substituted C6-C10-heteroaryl group. Further examples of pharmaceutically acceptable salts are described in “Remington’s Pharmaceutical Sciences” 17. ed. Alfonso R. Gennaro (Ed.), Mark Publishing Company, Easton, Pa., U.S.A., 1985 and in Encyclopedia of Pharmaceutical Technology. 
     Pharmaceutically acceptable solvates are for example hydrates. 
       FIG.  8    is a drawing that will now be used to illustrate operation of the supplemental device  2 .  FIG.  8    is part flowchart and part state diagram. 
     In the following, user inputs are denoted with reference numerals commencing “I”, displays or states are denoted with reference numerals commencing with “D”, and other elements of the drawing, for instance checks made by the supplemental device and explanatory information, are denoted by reference numerals commencing with “E”. 
     In the following, the display  21  is referred to as the LCD  21 , so as to avoid confusion between the hardware display  21  and the image that is displayed, and which may be termed a display. However, the LCD  21  may be any suitable form of display hardware. 
     Initially, the supplemental device is powered off. This provides the display shown in D 1 . 
     D 1  also goes to show the general arrangement of the user interface features of the supplemental device. In particular, an uppermost surface of the supplemental device  2  is shown provided with the LCD  21  and the confirm/OK button  34 . The confirm/OK button  34  is located to the left of the LCD  21  in this example, although it may have an alternative location in other embodiments. The power on/off button  22  and the communications button  33  are located on the side of the supplemental device  2 . As shown here, the communications button  34  and the power on/off button  22  are located on the same side of the supplemental device  2 , although in other embodiments the buttons are located differently. For instance, in some embodiments, the power on/off button  22  is located on the opposite side of the LCD  21  to the communications button  33 . In some other embodiments, the communications button  33  and/or the power on/off button  22  are located on the top surface of the supplemental device  2 . 
     At input I 1 , the user presses the power on/off button  22 . The input I 1  is detected by the supplemental device  2 . In particular, the processor  24  detects that the power on/off button  22  has been pressed for a relatively short period. Other user inputs are detected by the supplemental device in a similar manner, and short hand explanation is occasionally provided in the following explanation. In the following, ‘mode’ and ‘state’ are used interchangeably to denote the same thing; if the supplemental device  2  is in mode X it means the same as it being in state X. 
     If when the supplemental device  2  is in the state illustrated in D 1 , the supplemental device  2  receives a long press of the power on/off button  22 , denoted at input I 2  in  FIG.  8   , the supplemental device  2  transitions to the state or display shown at D 2 . Here, a power on progress bar is displayed on the LCD  21 . This progress bar includes a symbol denoting power or a battery and also includes an indicator relating to the power level of the battery. As shown in  FIG.  8   , the battery power is approximately one third of the full battery in this example. The supplemental device  2  remains in the state indicated by D 2  for a predetermined time, for instance  2  or 3 seconds. Following the state indicated in D 2 , the supplemental device  2  transitions to one of four possible states. 
     If the supplemental device is not mounted on the injection device  1 , as is detected by the supplemental device by the processor  24  examining a state of the detection switch  30 , the supplemental device  2  transitions to the state indicated by D 3  in  FIG.  8   . Here, the supplemental device provides on the LCD  21  a graphic indicating that no pen is present. This may be purely graphical, purely textural, or a combination of graphics and text. 
     If when the supplemental device  2  is in the state indicated by D 2 , the supplemental device  2  detects that there is not correct alignment between the supplemental device  2  and the injection pen  1 , the supplemental device progresses to the state indicated by D 4  in  FIG.  8   . An incorrect alignment between the supplemental device  2  and the injection device  1  may be detected by the supplemental device by examination of the symbols received by the OCR module  25  and/or the photometer  26 . 
     Thirdly, if the supplemental device when in the state indicated by D 2  detects that the battery  32  is almost empty, the supplemental device transitions to a low battery state indicated by D 5  in  FIG.  8   . Here, a battery warning graphic is provided. This may take any suitable form. 
     If the supplemental device  2  does not transition into any of the three states indicated by D 3 , D 4  and D 5  in  FIG.  8   , it transitions to the state indicated by D 6 . This is called the default state. In the default state, the supplemental device indicates details of the last injection. Put another way, in the default state, the supplemental device  2  displays information relating to the last use of the injection pen  1 . 
     The default state D 6  is also arrived at following the unmounted state indicated by D 3 , the incorrect alignment state indicated by D 4  or the low battery state indicated by D 5 . The supplemental device  2  may remain in any of these preceding states for a predetermined time, for instance 3 seconds, 5 seconds or 10 seconds, before transitioning to the default state, shown in D 6 . 
     In the case of the unmounted state indicated by D 3 , the supplemental device  2  may instead refrain from transitioning to the default state indicated by D 6  until the supplemental device  2  detects that there is correct alignment between the supplemental device  2  and the injection pen  1 . Alternatively, after the supplemental device has transitioned through the unmounted state indicated by D 3 , the supplemental device may remain in the default state indicated by D 6  until the supplemental device detects, by examining the state of the detection switch  30 , that the supplemental device  2  is mounted on the injection device  1 . 
     With respect to the unaligned state indicated by display D 4  in  FIG.  8   , the supplemental device  2  may remain in the unaligned state until the supplemental device  2  detects correct alignment between the supplemental device  2  and the injection device  1 . Alternatively, the supplemental device  2  may transition from the unaligned state indicated by D 4  to the default state indicated by D 6  but refrain from progressing from the default state until the supplemental device  2  detects that there is correct alignment between the supplemental device  2  and the injection device  1 . 
     If the supplemental device has transitioned through the low battery state indicated by D 5  before arriving at the default state indicated by D 6  in  FIG.  8   , the supplemental device  2  indicates periodically that there is a low battery state. This is achieved by a check step E 1  that depends from the default state D 6 . The check step E 1  involves the supplemental device  2  determining whether the battery  32  is almost empty and, if so, an action step E 2  involves providing the warning shown in the display D 5  periodically. 
     Even if the supplemental device  2  did not transition through the low battery state indicated by D 5  before arriving at the default state indicated by D 6 , the check step E 1  is performed periodically. Thus, when the supplemental device  2  is in the default state, indicated by D 6  in  FIG.  8   , and the battery level falls such that at the check step E 1  it is determined that the battery is almost empty, action step E 2  involves causing the supplemental device  2  to transition to the low battery state indicated by D 5 . 
     Once the low battery state D 5  has been transitioned through, the low battery display indicated by D 5  is provided periodically until the battery  32  is replaced or otherwise replenished. In some embodiments, the low battery display indicated in D 5  is provided only when the supplemental device  2  is in the default state. This prevents the low battery warning being provided to the user when the device is in use in connection with delivery of a dose of medicament and/or when the supplemental device  2  is attempting to communicate with another device. 
     Although not shown in  FIG.  8   , if when the supplemental device  2  is in the default state, indicated by D 6  in the Figure, the supplemental device  2  receives a long press of the power on/off button  22 , the supplemental device powers down. Thereafter, the device is in the off state that is indicated by D 1  in  FIG.  8   . The supplemental device  2  may be responsive to a long press of the power on/off button  22  to power down from any state. 
     The supplemental device  2  may transition from the default state indicated by D 6  in response to detecting that the user has turned the dosage dial  12 . This is indicated at I 3  in the Figure. In response, the supplemental device  2  enters a dosage dialling state, which is indicated at D 7  in  FIG.  8   . Here, the supplemental device  2  displays on the LCD  21  the dose medicament that is currently dialled into the injection pen  1 . This is known by the supplemental device  2  by virtue of reading of the  FIG.  19    from the injection device by the OCR reader  25 . In this state, the supplemental device  2  also displays an indication of the medicament that is present within the injection device  1 . In the display D 7 , the medicament is indicated through the display of text that names the medicament, in this case “Apidra”. 
     The currently set dose is indicated in the dosage dialling state in the display shown in D 7  in any suitable way. The dose advantageously is indicated in the largest characters that can be accommodated by the LCD  21 . In particular, the height of the letters may be equal to the height of the LCD  21 , or at least have a height that is  80  or 90% or more of the height of the LCD  21 . The supplemental device may provide the display D 7  in such a way as to make it clear to the user that the dose value displayed on the LCD  21  relates to a dose that is currently dialled into the injection pen in any suitable way. For instance, graphical elements provided around the displayed dose value may blink or flash. Alternatively, the characters of the dose value themselves may blink or flash. Alternatively, the background may blink or flash. 
     When the supplemental device  2  detects that the dosage dial  12  has not been turned for a predetermined period, for instance 0.5 seconds or 1 second, this is detected at input I3a (although it is actually absence of an input) and the supplemental device  2  transitions to a dose dialled state, which is indicated by the dialled dose display D 7   a  in  FIG.  8   . In the dose dialled state, the supplemental device  2  causes the LCD  21  to provide two different displays, with the device  2  transitioning from one display to the other display and back again on a periodic basis. In the dose dialled state indicated by D 7   a , both displays include the dialled dose, and this is provided in the same location. The dialled dose may be displayed in the same way in both of the displays. One display indicates the medicament that is present in the injection device  1 . In this example, this is indicated by text that names the medicament, in this case “Apidra”. The other display includes an indication that a dose of medicament may be delivered. In this example, this is provided by a graphic of a hand with a confirm/OK button. 
     If while in the dose dialled state illustrated by D 7   a  the supplemental device  2  receives an input relating to further turning of the dosage dial  12 , indicated by input I 3  in  FIG.  8   , the supplemental device again proceeds to the dosage dialling state that is indicated by D 7  in the Figure. 
     If the supplemental device  2  detects that the confirm/OK button  34  has been operated by a user when the device is either in the dosage dialling state indicated by D 7  or in the dose dialled state indicated by D 7   a , this input I 4  causes transition to an inject now state, which is indicated by D 8  in  FIG.  8   . In the inject now state, a graphic is provided indicating to the user that injection is possible. 
     At this stage, the user has two options. They may change the dose. This is achieved by the user selecting the confirm/OK button  34  and then turning the dosage dialler  12 . This is detected as an input I 5  by the supplemental device. In detecting the input I 5 , the supplemental device  2  reverts to the dose dialled state indicated by D 7  in  FIG.  8   . 
     Alternatively, the user can inject the medicament. This is detected by the supplemental device  2  as an input I 6 . Input I 6  causes transition to a dosage delivery state, indicated as D 9  in  FIG.  8   . Here, the dose remaining dialled into the injection device  1  is displayed on the LCD  21 . As the dose is delivered, the dose remaining becomes smaller. As such, the remaining dose value counts down from the dialled in dose towards zero. 
     If the user does not deliver the entire dose, this is detected by the supplemental device at input I 7  either by detecting depression of the confirm/OK button  34  or by detecting that the user has turned back the dosage dialler  12 . The input I 7  causes transition to a ten second countdown state, indicated at the display D 10  in the Figure. After the ten seconds have lapsed, the supplemental device  2  transitions to a partial dose delivered state, indicated by a display D 11  in  FIG.  8   . Here, the supplemental device  2  displays the dose delivered to the user through the injection pen  1 . The dose delivered is equal to the dose that was dialled in, as detected by the supplemental device when in the dosage dialling state indicated by D 7  or the dialled dose state indicated by D 7   a , minus the dose remaining when the input I 7  was detected. In this state, the medicament that was delivered also is displayed. In this example, the delivered dose is indicated in characters that are smaller than the characters provided by either of the states indicated by D 7  and D 7   a  in  FIG.  8   . Arranged vertically with respect to the delivered dose is an indication of the medicament that was delivered. On transitioning to or from this state, a timer (not shown) within the supplemental device is reset. The timer allows the supplemental device  2  to calculate an elapsed time since a last dose was delivered. Transition from the state indicated by display D 11  is to the state indicated by D 7  in  FIG.  8   . 
     Alternatively, the supplemental device  2  may exit the dose delivery state indicated by D 9  by detecting an input I 8  indicative of the injection having been completed. In this case, the supplemental device transitioned to a countdown state that is indicated by the display D 12  in  FIG.  8   . Here, the LCD  21  is provided with an icon that is the same as the icon provided in the display of the countdown state indicated by D 10  in the Figure. 
     After ten seconds have elapsed, the supplemental device  2  transitions to a remove needle instruction state, indicated at the display D 13  in  FIG.  8   . Here, the supplemental device  2  provides a graphic that indicates to the user that the needle of the injection device  1  should be replaced. After a predetermined time, or upon detecting that the needle has been replaced if the acoustical sensor  27  is present, the supplemental device  2  transitions to a reset state that is indicated by the display D 14  in  FIG.  8   . Here, the value of the delivered dose is stored in the supplemental device  2  and a timer (not shown) is started. The timer provides a value that is indicative of the time elapsed since the last dose. After the reset state, the supplemental device  2  transitions to the default state, indicated by D 6  in  FIG.  8   . 
     If when the supplemental device  2  is in the default state, indicated by D 6 , it detects an input I 9  indicating that the user has pressed the communication button  33 , it transitions from the default state. Here, the supplemental device  2  determines whether a device is accessible. A device here is for instance the blood glucose measurement unit  42 . If a determination at step S 3  indicates that a device is accessible and it is determined in E 4  that the device is unknown, the supplemental device  2  enters a pairing process state, which is indicated by D 15  in the Figure. In this state, the supplemental device  2  initiates pairing with the detected device. In the case of the wireless unit  28  being a Bluetooth transceiver, this involves initiating pairing in accordance with the Bluetooth standard. In the pairing process state, indicated by D 15 , a Bluetooth PIN number is displayed on the LCD  21 . This is accompanied with an icon requesting that the user confirm that the PIN number matches with one displayed on the unknown device. If the supplemental device  2  determines at E 5  that pairing has failed, the supplemental device  2  transitions to a Bluetooth error message state, indicated by D 16  in the Figure. This state is also transitioned to following input I 9  if it is determined at E 8  that no device is accessible. In the Bluetooth error message state, indicated by D 16 , an icon is displayed on LCD  21  indicating that no communication is possible. Following the Bluetooth error message state, for instance after a predetermined time, the supplemental device  2  transitions to the default state, indicated by D 6 . 
     If in the pairing state the supplemental device at E 6  determines that pairing has been completed, it transitions to a short transmission state, indicated by D 17 . The supplemental device also transmissions to the short transmission state indicated by D 17  from the default state indicated by D 6  following input I 9  if the supplemental device determines that a device is accessible at E 3  and at E 7  determines that it is a known device. 
     In the short transmission state, indicated by D 17 , an icon or graphic is displayed on the LCD  21  indicating that communication is in process. Once communication is complete, the supplemental device  2  transitions to a transmission done stage, indicated by D 18 . Here, the supplemental device  2  provides a graphic indicating that transmission has been completed. Following the transmission done state, the supplemental device  2  transitions to the default state, indicated by D 6 . 
     When in the default state, indicated by D 6 , operation is as follows. The supplemental device  2  is expected to be in the default state for most of the time for which it is powered on. As such, the displays D 6  when in the default state are the displays that are likely to be seen most by a user of the supplemental device. 
     When in the default state, the supplemental device is configured to indicate to the user details of the last delivered dose. The details include the quantity of the dose and the time elapsed since the last dose delivery. These details also include the identity of the medicament. 
     In these embodiments, this is achieved by transitioning between two different displays in the default state. The first display is shown uppermost in display D 6  in  FIG.  8   . Here, it will be seen that there are two regions of the LCD  21 . A region on the left side occupies approximately two thirds of the area of the display. This region is hereafter termed the last dose region. On the right side of the LCD  21 , to the right of the last dose region, is another region. The other region in this example displays a dose that is dialled into the injection pen  1 . The information displayed on the right side of the LCD  21  is the dialled value from the injection pen  1 . This is not influenced by the information displayed on the left side of the LCD  21 . 
     The last dose region in the first display, shown uppermost in D 6  in  FIG.  8   , is divided into two areas. Here, they are upper and lower areas. In a first area, here the lower area, the last delivered dose is displayed. This is in the form of a number, indicating the dose in IUs. 
     In the second area, the elapsed time since the last dose delivered is displayed. Here, this is displayed as a time expressed as a number and with a unit of time expressed in Roman characters. Display of the unit of time allows a user to distinguish between the display of the time since the last dose and the quantity of the dose. The second area also includes a graphic indicating a timer or clock, which reinforces this message. 
     In the second display, shown lowermost in D 6  in  FIG.  8   , the first area is unchanged. The first area thus displays the quantity of the last dose. The second area does not show the time elapsed since the last dose. Instead, it shows the medicament of the last dose. Here, this is indicated by text that spells the name of the medicament, in this case “Apidra”. The clock or timer icon is again displayed in the second area. 
     In the default state, the supplemental device  2  causes the display to transition between the first and second displays, shown uppermost and lowermost respectively, periodically. Transitioning may occur every two seconds, for instance. 
     As can be seen in  FIG.  8   , the first area of the dose display region  21 B is larger than the second area. As such, the height of the characters used to indicate the quantity of the dose are larger than the characters used to indicate the time elapsed since the last dose or the identity of the medicament. As such, a user is able to determine quickly and easily, perhaps with only a glance, the quantity of the last dose. 
     Additionally, the user is able to determine relatively easily the time elapsed since the last dose. It is the time elapsed since the last dose and the quantity of the dose that are the parameters that are most of interest to users of medicaments that are used to treat diabetes. It is these parameters that are most of interest to the user when determining the next dose of medicament, in terms of the time when it should be delivered and in terms of the quantity of medicament that may be needed. 
     As such, the provision of the default state and the displays provided in that state by the supplemental device  2  can allow the user better to treat the condition for which the medicament is prescribed. Put another way, the features of the supplemental device when in the default state can allow the user more easily to treat their condition, potentially providing better treatment for the user. 
     An alternative embodiment will now be described with reference to  FIGS.  2   c  and  9   . 
     As can be seen in  FIG.  2   c   , the supplemental device  2  is provided with a LCD  21  and a power on/off button  22 . The LCD  21  is a touch-sensitive display, through which a user can provide input to the supplemental device. As such, the touch-sensitive LCD  21  also provides the functions provided by the communications button  33  and the confirm/OK button  34  in the embodiment of  FIG.  8    and  FIG.  2   b   . 
     Operation of the supplemental device according to this embodiment is quite similar to the operation of the device of  FIG.  2   b   , as described with reference to  FIG.  8   . In  FIG.  9   , reference numerals are retained from  FIG.  8    for like elements, and only the differences between operation of the embodiment of  FIG.  2   c    and the embodiment of  FIG.  2   b    will be described here. For features and operation of the device of  FIG.  2   c    that are the same as features and operations of the device of  FIG.  2   b    and  FIG.  8   , no discussion is made in the following. 
     The device off state, illustrated by display D 1  in  FIG.  9    is very similar to the corresponding state of the device operation shown in  FIG.  8   . This display D 1  illustrates the overall layout provided on the LCD  21 . In particular, a first region  21 B of the display is a display region  21 B. This is shown on the right of the display of D 1  of  FIG.  9   . A second region  21 A of the display is an input region  21 A. This is shown on the left in D 1 . The input region  21 A is also an active display region  21 B. However, the input region  21 A is a region where user inputs may be received. The input region  21 A includes a display of a virtual button at appropriate times, in particular when the supplemental device  2  is in certain states. The input region  21 A in this embodiment is always located in the same place on the LCD  21 . This simplifies the experience for the user. In other embodiments, the input region  21 A may change in location depending on the state of the supplemental device. The input region  21 A is the touch sensitive input  35  shown in  FIG.  2   c   . 
     In the device off state shown in D 1 , the LCD  21  is blank. When the LCD  21  is blank in a region, nothing is displayed in that region. When the input region  21 A is blank, an outline of the virtual button may be displayed, although nothing is displayed within the virtual button. 
     In the power off progress state shown by D 2 , the input region  21 A is left blank, that is nothing is displayed in the input region  21 A. In this state, the display region  21 B is provided with an indicator that indicates the amount of power remaining in the battery  32 . This indicator is the same as the indicator shown in D 2  of  FIG.  8   , although it is smaller in size. 
     In the device not mounted state D 3 , the input region  21 A is blank, and a graphic indicating that the pen is not connected is shown in the display region  21 B. In the camera adjustment issue state shown at D 4 , the input region  21 A is left blank and the display region  21 B indicates that there is not alignment between the supplemental device  2  and the injection device  1 . In the battery low state indicated by display D 5 , the input region  21 A is left blank and the display region  21 B includes an icon indicating that the battery is almost empty. 
     In the default state, the input region  21 A is provided with an icon relating to communication options. In this example, the input region  21 A is provided with an icon indicating a Bluetooth communication option. The supplemental device  2  is configured when in the default state to respond to a user input I 9  comprising touching of the LCD  21  at the input region  21 A to proceed through the checks E 3  and E 8 , as described above with reference to  FIG.  8   . 
     When in the default mode, the display region  21 B of the display is provided with the displays as described above in relation to the first region of the display in the default state of  FIG.  8   . 
     If the supplemental device  2  detects that the battery is almost empty when the device is in the default state shown by D 6 , the check E 1  may cause an action E 2  which results in transitioning of the device to the battery almost empty state, providing a display shown in D 5 , periodically. Alternatively, the supplemental device  2  may be configured to include a low battery icon within the display region  21 B. This is indicated by the display D 19  in  FIG.  9   . 
     When in the currently set value state indicated by the display D 7  in  FIG.  9   , the currently dialled dose is displayed in the display region  21 B. The input region  21 A is provided with a graphic, which in this case is the word “OK”. When in this mode, the supplemental device  2  is responsive to detection of a user input at the input region  21 A of the LCD  21 , represented by input I 4  in  FIG.  9   , to transition to the inject now state, illustrated by display D 8  in  FIG.  9   . In the inject now state, the input region  21 A is provided with an indication of the dialled dose. The display region  21 B is provided with an icon which is the same as the icon shown in D 8  of  FIG.  8   . After an injection input I 8 , the number displayed within the input region  21 A counts down, reflecting the remaining dialled dose. 
     The supplemental device  2  is responsive to detection of a user input at the input region  21 A of the LCD  21 , indicated by input I 7  in  FIG.  9   , to transition to the countdown state indicated by D 10  in the Figure. 
     In the display indicated by display D 11  in  FIG.  9   , the delivered dose is displayed, along with an indication of the medicament delivered. 
     In the countdown states indicated by the displays D 10  and D 12  in  FIG.  9   , the input region  21 A of the LCD  21  is left blank. This is the case also for the remove needle state instruction provided by D 13  in  FIG.  9   . In these states, no transition occurs from user input, so it is appropriate for the input region  21 A of the LCD  21  to remain blank. 
     The communication error message state, indicated by D 16 , is similar to the corresponding display of  FIG.  8   . However, the input region  21 A of the LCD  21  includes the text “OK”. The supplemental device  2  is configured to transition from the communication error message state shown by D 16  to the default state shown by D 6  after a predetermined time or upon detecting a user input at the input region  21 A of the LCD  21 . 
     The text “OK” is provided at the input region  21 A of the LCD  21  also when in the pairing state, indicated by display D 15  in  FIG.  9   . The supplemental device  2  is configured to respond to detection of a user input at the input region  21 A of the LCD  21  to transition either to the communication error message state shown by D 16  or the short transmission state indicated by D 17  depending on whether pairing has been achieved. Alternatively, transitioning may occur automatically, for instance in response to detection of a time out. 
     It will be appreciated from the above description of  FIG.  9    that operation of the supplemental device of  FIG.  2   c    is quite similar to the operation of the device of  FIG.  2   b   . However, the dynamic adjustment of the text or graphics control to be displayed in the input region  21 A of the LCD  21  simplifies the process of use for the user. In particular, aside from the power on/off button  22 , there is only ever one input button/region  21 A that needs to be operated by the user. Moreover, the consequence of the user operating the input should be more obvious. 
     Additionally, the arrangement of the supplemental device  2  of  FIG.  2   c    is such that the user cannot operate the communications button other than when the device is in the default state, indicated by D 6 . This prevents the user believing that the supplemental device  2  might lead to actuation of the communications button  33  other than when in the default state, shown by D 6 . 
     It will be appreciated that the above-described embodiments are merely examples and that numerous alternatives will be envisaged by the skilled person and are within the scope of the present invention. 
     For instance, the communication states etc may be replaced by alternative states in which operation of the supplemental device  2  is quite different, or these states may be omitted altogether. 
     Referring to  FIGS.  10  and  11   , embodiments of the invention will now be described.  FIG.  10    shows a lateral cross-section taken through the injection device  1  with supplemental device  2  attached. In  FIG.  10   , only the central part of the supplemental device  2  is shown; the mating unit which embraces the injection device  1  is omitted for clarity.  FIG.  11    shows an axial cross-section taken through the injection device  1  with supplemental device  2  attached. Some components of the supplemental device are omitted or shown in wireframe in  FIG.  11    for clarity. 
       FIGS.  10  and  11    both show an electromechanical switch arrangement  110 . In  FIG.  10   , the remained of the supplemental device  2  is not shown. The electromechanical switch arrangement  110  comprises a self-contained unit which is fitted to the supplemental device  2 . The electromechanical switch arrangement  110  may for example be housed in a recess in the underside of the supplemental device  2  (the part which contacts the injection device  1 ). The electromechanical switch arrangement  110  may be secured to the supplemental device  2  by friction or by an interlocking arrangement (not shown), or alternatively by screws, adhesive or the like. 
     The electromechanical switch arrangement  110  comprises a main body  111  (also referred to herein as a housing  111 ). A cavity is defined inside the main body  111 . An upper part of the main body  111  is arranged to engage with the housing  20  of the supplemental device  2  to secure the electromechanical switch arrangement  110  to the supplemental device  2 . A lower part of the main body is concave in shape and matches the curvature of the injection device  1 . The lower part of the main body  111  has an aperture. 
     In embodiments of the invention, the injection device  1  to which the supplemental device  2  is to be attached has a corrugated dialling sleeve  119 . The corrugations are defined by troughs  116  and crests  117 . The dialling sleeve  119  is configured to rotate with the dosage knob  12  during dose dialling. The dialling sleeve  119  may be coupled directly to the injection button  11 . The lower part of the main body  111  of the electromechanical switch arrangement  110  abuts several of the crests  117  of the corrugated dialling sleeve  119  but the dialling sleeve  119  is free to rotate relative to the electromechanical switch arrangement  110 . 
     A switch  113  (also referred to as a switching member  113  or switching lever  113 ) is rotatably mounted inside the main body  111  of the electromechanical switch arrangement  110 . The switch  113  has a protrusion  118  and is arranged such that this protrusion passes through the aperture in the main body  111  and protrudes from the main body  111 . An internal spring  114  biases the switch  113  towards the position shown in  FIG.  10   , in which the switch  113  abuts an internal surface of the main body  111  and the end of the protrusion  118  abuts a trough  116  of the dialling sleeve  119 . The internal spring  114  may for example be a torsion spring. In some embodiments, the injection device  1  is configured such that a small portion of the dialling sleeve  119  adjacent the dosage button  12  extends out of the housing  10  of the injection device  1  when no dose has been dialled. This allows the protrusion  118  to contact the dialling sleeve  119  at all times during operation of the device. 
     The inner wall of the electromechanical switch arrangement  110  comprises two electrical contacts  112 . These contacts are arranged to be engaged by corresponding electrical contacts on the switch  113 . In some embodiments, the contacts  112  and/or the corresponding contacts on the switching member  113  are sprung contacts. For example, a first of the contacts  112  may be engaged at all times by a contact on the switch. A second of the contacts  112  is not engaged by the switch  113  when in the position shown in  FIG.  10   . This second contact  112  is engaged by the switch  113  only when the protrusion  118  of the switch  113  rides up a crest  117  of the dialling sleeve  119 , causing the switch to rotate within the main body  111 . When the switch  113  engages this second contact, an electrical connection is made through the switch between the two contacts  112 . As previously described, the supplemental device  2  comprises a processor  24 . This processor  24  is configured to control the application of a signal to one of the contacts  112  and to detect when the circuit is completed by measuring a signal at the other of the contacts  112 . 
     The supplemental device  2  also comprises a compensation spring  115  (also referred to herein as a biasing member), visible in  FIG.  11   . The compensation spring  115  forms part of the supplemental device  2 , but is external to the electromechanical switch arrangement  110 . The compensation spring  115  may be a torsion spring. The compensation spring  115  has a first end  120  which is secured internally to the housing  20  of the supplemental device  2 . The concave underside of the supplemental device  2  is shown in wireframe in  FIG.  11   . The compensation spring  115  has a second end  121  which is secured to the electromechanical switch arrangement  110 . The second end  121  of the compensation spring  115  may be secured to an upper part of the electromechanical switch arrangement  110  (relative to the orientation of shown in  FIG.  11   ). The compensation spring  115  exerts a force on the electromechanical switch arrangement in the direction of the arrow “A” on  FIG.  11   . This force causes the electromechanical switch arrangement  110  to be biased towards the injection device  1  and in particular towards the dose dialling sleeve  119 . 
     The compensation spring  115  may compensate for relative movement between the supplemental device  2  and injection device  1  and/or between the electromechanical switch arrangement  110  and supplemental device  2  as described in greater detail below. These relative movements may be due to manufacturing tolerances of the supplemental device  2 , electromechanical switch arrangement  110  and injection device  1 , in particular the dose dialling sleeve  119 , or may be an intentional design feature. 
     Exemplary operation of the injection device  1  and supplemental device  2  containing the electromechanical switch arrangement  110  will now be described. 
     First the electromechanical switch arrangement  110  is secured to the supplemental device  2 . This may be done during manufacture of the supplemental device  2 . A user then fits the supplemental device  2  to the injection device  1  as previously described. Once the supplemental device  2  has been fitted to the injection device  1 , the lower part of the electromechanical switch arrangement  110  abuts the surface of the injection device  1 . 
     When a dose has been dialled into the injection device  1 , the electromechanical switch arrangement  110  abuts the dose dialling sleeve  119 , as depicted in  FIGS.  10  and  11   . The concave underside of the electromechanical switch arrangement  110  contacts several crests  117  of the corrugated surface of the dialling sleeve  119 . The dose dialling sleeve  119  has a smaller diameter than the outer housing  10  of the injection device  1  and may have the same or a smaller diameter than the dosage knob  12 . 
     Due to the action of the internal spring  114 , the protrusion  118  of the switching member  113  is forced to protrude through the aperture in the main body  111  of the electromechanical switch arrangement  110 . Thus the protrusion  118  may contact a trough  116  of the dose dialling sleeve  119  while the electromechanical switch arrangement  110  rests on the crests  117  of the sleeve. 
     A user then dials in a dose by grasping and rotating the dosage knob  12 . The dose dialling sleeve  119  rotates relative to the supplemental device  2 . As the sleeve  119  rotates, the protrusion  18  of the switching member  113  follows the contours of the dialling sleeve surface. When a crest  117  is rotated past the aperture, the protrusion  118  rides up the crest, forcing the switching member  113  to rotate within the main body  111 . The switching member  113  contacts the second of the contacts  112  when the protrusion  118  reaches the top of a crest  117 . The switching member  113  may be in contact with the first of the contacts  112  at all times. An electrical path is formed between the two contacts  112  when the switching member  113  engages with the second of the contacts  112 . The processor  24  detects that the switch has been closed by applying a signal at the first contact and measuring a signal at the second contact. 
     As the sleeve continues to rotate, the protrusion  118  rides down the crest  117  and into the next trough  116  under action of the internal spring  114 . The switching member  113  ceases to contact the second contact  112 . The processor  24  determines from this sequence that one unit (IU) has been dialled into the injection device  1 . For each unit which is dialled into the injection device  1 , the processor detects one connection of the circuit preceded and followed by a disconnection. 
     The switching point of the electromechanical switch arrangement  110 , i.e. the point at which the switch  113  completes a circuit between the two contacts  112 , occurs when the protrusion  118  rides up to the top of a crest  117 . The contacts  112  may be sprung contacts to allow some range in the switching point. However, relative movement between the supplemental device  2  and injection device  1  and/or between the electromechanical switch arrangement  110  and supplemental device  2  may mean that the switching point is not reached when the protrusion  118  reaches the top of a crest  117 . This may be a result of manufacturing tolerances of the injection device  1 , supplemental device  2  and electromechanical switch arrangement  110 . 
     The compensation spring  115  compensates for these tolerances by forcing the main body  111  of the electromechanical switch arrangement  110  against the dose dialling sleeve  119  surface. For example, the electromechanical switch arrangement  110  may be secured to the supplemental device  2  at only a single point, allowing some lateral or rotational movement between these two components. The supplemental device  2  may also have some degree of movement relative to the injection device  1 , even while secured to the injection device. The effect of any manufacturing tolerances of these components is therefore removed. 
     The user then delivers the selected dose. During this procedure, the dose dialling sleeve  119  moves back into the injection device  1 , but does not rotate. The dose dialling sleeve  119  is disconnected from the sleeve  19  and dosage knob  12  by an internal clutch coupled to the injection button  11 . Alternatively, the dose dialling sleeve  119  may be coupled directly to the injection button, which is itself disconnected from the sleeve  19  and dosage knob  12  by the internal clutch. Thus during dose delivery, the protrusion  118  of the switching member  113   remains in the same trough  116  of the dose dialling sleeve  119  and no circuit connection is made by the switching member  113 . 
     The electromechanical switch arrangement  110  is provided in addition to the OCR reader  25 . If the processor  24 , using the OCR reader  25 , detects that the numbers on the sleeve  19  are changing, it is important also to determine whether a dose is being dialled in (dose setting), dialled out (dose correction) or delivered (dose dispense). This determination is not possible using the OCR reader  25  alone. Use of the electromechanical switch arrangement  110  allows this determination to be made. 
     The OCR reader  25  of this embodiment is one possible implementation of a dose dialled detector operable to detect a dose of medicament dialled into the attached injection device. Other implementations are feasible, using a position determination system for a member that moves when a dose is dialled, wherein the positioning system comprises electrical contacts, optical encodings, or magnetic particles. The electromechanical switch arrangement  110  according to this invention is provided in addition to the dose dialled detector. If the processor  24 , using the dose dialled detector, detects that the dose is changing, it is important also to determine whether a dose is being dialled in (dose setting), dialled out (dose correction) or delivered (dose dispense). This determination is not possible using the dose dialled detector alone. Use of the electromechanical switch arrangement  110  allows this determination to be made. 
     If the processor  24  determines that the numbers detected by the OCR reader  25  are increasing and also that the electromechanical switch arrangement  110  is being alternately opened and closed, it can be deduced that a dose is being dialled into the injection device  1 . If the processor  24  determines that the numbers detected by the OCR reader  25  are decreasing and also that the electromechanical switch arrangement  110  is being alternately opened and closed, it can be deduced that a dose is being dialled out of the injection device  1 , without being delivered. If the processor  24  determines that the numbers detected by the OCR reader  25  are decreasing and also that no connection is made in the electromechanical switch arrangement  110 , it can be deduced that a dose is being delivered. 
     The electromechanical switch arrangement  110  may also be used to activate and control additional switching functions. This functionality will now be described with reference to  FIGS.  12   a  and  12   b   .  FIG.  12   a    shows diagrammatically the arrangement of some components of the injection device  1  and supplemental device  2  when no dose is dialled into the injection device. The dose dialling sleeve  119  is in the zero position. A zero appears in the window  13 . The window  13  is in view of the OCR reader  25  which, under control of the processor  24 , determines that no dose is dialled in. The dose dialling sleeve  119  extends from the housing  10  of the injection device by a distance large enough to allow the protrusion  118  of the switching member  113  to contact the surface of the sleeve  119 . The injection device  1  may be configured such that this spacing cannot be reduced further by rotating the dosage knob  12 . The protrusion  118  of the switching member  113  engages with a trough  116  while in this position. As a result the electromechanical switch arrangement  110  does not form a connection between the two contacts  112 . Each trough  116  of the dose dialling sleeve  119  ends at the dosage knob  12  end with an axial ramp  122 . 
     The processor  24  may determine that, if the OCR reader  25  detects a zero value, or, alternatively, a dose dialled detector as described above detects a zero position of the dose dialling sleeve  119 , and the electromechanical switch arrangement  110  has not formed a connection, that the injection device  1  is not currently being used. After a predetermined time delay, the processor  24  may put the supplemental device  2  into a sleep mode. 
     As previously described, the injection button  11  and dose dialling sleeve  119  are coupled to an internal clutch (not visible) which disconnects these parts from the dosage knob  12  when the injection button  11  is depressed. The clutch is sprung so as to bias the injection button  11  in an un-depressed position. During dose delivery, the injection button  11  must be fully depressed before the clutch is disengaged, allowing the dose to be delivered. Thus the injection button  11  and dose dialling sleeve  119  are able to move axially relative to the other components of the injection device  1  by an amount corresponding to the distance over which the clutch remains engaged. 
       FIG.  12   b    shows diagrammatically the arrangement of some components of the injection device  1  and supplemental device  2  when the injection button  11  is depressed when no dose is dialled in to the injection device. Both the injection button  11  and dose dialling sleeve  119  move in the direction of the arrow “B” when the injection button  11  is depressed. The protrusion  118  ascends the axial ramp  122  causing the switch  113  to rotate which causes an electrical connection to be made between the contacts  112  in the electromechanical switch arrangement  110 , i.e. the switch is closed. If the user releases the force on the injection button  11 , the bias of the clutch causes the injection button  11  and dose dialling sleeve  119  to return to the position shown in  FIG.  12   a   , in which the switch is open. This arrangement allows other functions of the supplemental device  2  to be controlled by the electromechanical switch arrangement  110 , via the injection button  11  of the injection device  1 . 
     The electromechanical switch arrangement  110  can be used as a “dispense-end” switch. During dispensing, the protrusion  118  remains in a trough  116  of the dose dialling sleeve  119  such that the switch is open. If the user continues to apply force to the injection button  11  after all of the dose has been delivered, the protrusion  118  ascends the axial ramp  122  and the switch  110  is closed. When the user releases the force, the switch is opened again. The processor  24  detects this closing and opening of the switch and determines that the dose has been fully administered. The processor  24  may then control the supplemental device  2  to enter a dispense-end mode and control the display  21  to show an appropriate screen. 
     If the supplemental device  2  is in a sleep mode, for example because it has been determined that the injection device  1  is not being used, the electromechanical switch arrangement  110  may be used as a “wake-up” switch. The processor  24  may be configured to monitor the electromechanical switch arrangement  110  while in sleep mode. If the user depresses the injection button  11 , the switch is closed. The processor detects this action and turns the supplemental device  2  on. The supplemental device  2  enters a default mode when switched on in this manner. In the default mode the dose dialled detector may be activated and ready and/or operable to detect a dose that has been dialled. 
     The electromechanical switch arrangement  110  can also be used as a “menu-select” switch. If the supplemental device  2  is on, but no dose has been dialled in, the closing of the switch by depressing the injection button  11  causes the processor  24  to cycle through the menu options of the supplemental device  2 . 
     Integrating these additional switching functions with the injection button  11  of the injection device  1  simplifies the use of the supplemental device  2  for a user. 
     The switching member  113  is described above as rotationally mounted. However, it may instead move in another way within the electromechanical switch arrangement  110 , for example by sliding vertically. The internal spring  114  may be disposed in the centre of the switching member to bias it towards the aperture in the main body  111 . The compensation spring  115  may alternatively be a coil spring or another type of biasing means. Instead of being located adjacent to the electromechanical switch arrangement  110 , the compensation spring  115  may be located above the electromechanical switch arrangement  110 , for example in a cavity between the housing  20  of the supplemental device  2  and the main body  111  of the electromechanical switch arrangement  110 . The switch  110  is described as being closed when the protrusion  118  ascends a crest of the corrugated dialling sleeve  119  or when the protrusion ascends the axial ramp  122  and open at all other times. However, the switch  110  may alternatively be opened when the protrusion ascends a corrugation or the axial ramp  122  and closed at all other times. Thus the processor may detect either state (or sense) change in the switch  110  and interpret this change as described above. n open state and a closed state , the electromechanical switch arrangement comprising a protrusion configured to contact a surface of the injection device while the supplemental device is attached to the injection device; a dose dialled detector operable to detect a dose of medicament dialled into the attached injection device; and a processor arrangement configured to: monitor the detected dose of medicament dialled into the attached injection device; detect a change in the state of the electromechanical switch arrangement; and change a display output of the supplemental device when a change in the state of the electromechanical switch arrangement is detected while a zero dose is dialled into the attached injection device.