PATENT DOCUMENT

Publication Number: US-9354612-B1
Application Number: US-201414279282-A
Country: US
Kind Code: B1

Title: Distributed time synchronization system and method

Abstract:
A system and method is disclosed for synchronizing device time on various electronic devices. The method and system weigh various factors such as origin of timing signals and elapsed time since last update to determine the most accurate synchronization time.

Claims:
What is claimed is: 
     
       1. A method for synchronizing device time among a plurality of electronic devices in a local area network comprising the operations of:
 prompting one or more of the electronic devices to update a device time in response to a triggering event; 
 polling each of the electronic devices to determine the origin of the previous device time update of each of the electronic devices; 
 querying each of the electronic devices to determine the amount of elapsed time since the previous device time update in each of the electronic devices; 
 scoring the accuracy of the device time of each of the electronic devices based upon the operations of polling and querying; 
 selecting the most accurate device time based upon the operation of scoring; and 
 updating the device time on each of the electronic devices to the most accurate device time. 
 
     
     
       2. The method of  claim 1  wherein the triggering event includes a user accessing a calendar on one of the plurality of the electronic devices. 
     
     
       3. The method of  claim 1  wherein the operation of scoring includes determining the number of times that the device time in each of the electronic devices has been updated in a time period. 
     
     
       4. The method of  claim 1  wherein the triggering event includes detecting a plurality of the electronic devices. 
     
     
       5. The method of  claim 1  wherein the triggering event includes determining the absence of a GPS signal for a predetermined time. 
     
     
       6. The method of  claim 1  wherein the triggering event includes detecting that the electronic device has entered a different local area network. 
     
     
       7. The method of  claim 1  wherein the triggering event includes detecting motion of the electronic device. 
     
     
       8. The method of  claim 1  wherein the triggering event includes detecting a time of day. 
     
     
       9. The method of  claim 1  wherein the triggering event includes detecting an adjacent electronic device within a predetermined distance. 
     
     
       10. The method of  claim 1  wherein the triggering event includes detecting a GPS signal. 
     
     
       11. A system for updating device time on a plurality of electronic devices comprising:
 a local area network electromagnetically connected to the electronic devices; 
 a crystal controlled oscillator in each of the plurality of the electronic devices; 
 a computer control device in each of the plurality of electronic devices; 
 a time display device in each of the plurality of electronic devices; and 
 wherein said computer control device selects a most accurate device time from among a device time on each of the plurality of electronic devices based upon the origin of and the amount of elapsed time since the last update of the device time on each of the plurality of electronic devices. 
 
     
     
       12. The system of  claim 11  wherein the plurality of electronic devices are located in a room in a building. 
     
     
       13. The system of  claim 11  wherein the computer control device in each of the plurality of electronic devices determines the accuracy of the device time in that electronic device based upon the frequency and amount of prior device time updates in that electronic device. 
     
     
       14. The system of  claim 11  wherein each of the plurality of electronic devices includes a sensor for detecting a triggering event. 
     
     
       15. The system of  claim 14  wherein the sensor includes an accelerometer. 
     
     
       16. A method for synchronizing device time displays on a plurality of electronic devices in a local area network comprising the operations of:
 determining an accurate device time from among a plurality of device times in the plurality of electronic devices, the operation of determining including:
 polling each of said electronic devices to determine the origin of the last device time update of each of the electronic devices; and 
 querying each of the electronic devices to determine the time of the last device time update of the electronic device. 
 
 
     
     
       17. The method of  claim 16  further including the operation of updating the device time on each of said electronic devices to the most accurate device time. 
     
     
       18. The method of  claim 16  wherein the origin of at least one of the device times is a GPS time signal. 
     
     
       19. The method of  claim 16  further including the operation of determining the number of times that the device time in each of the electronic devices has been updated in a time period. 
     
     
       20. The method of  claim 16  further including the operation of sensing a triggering event.

Description:
FIELD 
     The described embodiments relate generally to portable electronic devices such as laptop computers, phones, and tablets. More particularly, the present embodiments relate to synchronization of timekeeping on portable electronic devices. 
     BACKGROUND 
     Time is an important element in the daily lives of most individuals. Many meetings and other events require that the individual arrive in a timely manner Many individuals wear an electronic wristwatch or carry an electronic timepiece in their pocket or purse. Other individuals choose to rely on other portable electronic devices such as laptop computers, portable tablets and portable phones to provide the correct time. Many individuals utilize an electronic calendar in various types of electronic devices to remind them of meetings and events. Reliance on such devices has become an important part of the daily lives of many individuals, both in a business and personal setting. 
     Many kitchen appliances, test and measurement equipment, such as signal generators, and most portable electronic devices, such as cellphones, clocks, radios, and digital watches, keep time using quartz crystal controlled oscillators. A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. Digital logic is used to count the cycles of the signal and to provide a time display in the form of hours, minutes and seconds. The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits incorporating them are often referred to as crystal oscillators. Because of their compact size and because they are relatively inexpensive, quartz crystal is generally recognized as the most widely employed system of timekeeping in the world today. 
     Quartz crystal oscillators are generally accurate to approximately ±15 seconds per month. Environmental factors such as temperature, humidity, pressure and vibration, as well as battery voltage and age of the quartz crystal, typically influence the accuracy of a device&#39;s timekeeping. Methods and systems such as thermal compensation have been employed in an attempt to compensate for the environmental factors affecting the accuracy of quartz crystal oscillator timekeeping devices. Other types of materials such as ceramics may be used in some instances to replace quartz but those materials may also have their accuracy affected by various environmental factors. 
     Several techniques already exist to synchronize devices to a common time base, such as use of the Network Time Protocol (NTP) to synchronize to atomic clocks over the Internet, or use of a Global Positioning System (GPS) receiver to synchronize to the time signal transmitted by each GPS satellite. Typically, these techniques require Internet connectivity or GPS satellite reception, and so will not work under some circumstances. For example, a device that is outdoors may have access to GPS time, while a device that is indoors may only have access to the NTP system. 
     Because of a desire to have time synchronization among a variety of electronic devices in relative close network proximity it would be desirable to have a method and system which allows for accurate time synchronization among a group of electronic devices under varying conditions. 
     SUMMARY 
     Generally, embodiments described herein may facilitate synchronization of time between various electronic devices. The time synchronization may occur between devices connected to one another through a local transmission protocol, such as Bluetooth, an infrared transmission, and/or a radio frequency transmission, through devices connected to one another via a network protocol or local network, and through devices connected to one another through a longer-range protocol, such as the Internet. Time synchronization may likewise occur between devices that are physically connected to one another, for example with a cable or other connector. 
     Individually, suitable electronic devices may attempt to periodically synchronize themselves to GPS time, as this is generally the most accurate time available. Non-GPS enabled devices may attempt to synchronize time with a NTP or other network-available source. The interval between attempts may be chosen based on the overall desired accuracy. For example, assuming the device time is accurate to ±0.5 seconds per day, then 5 synchronization events per day would be needed to keep the device time accurate to ±0.1 seconds. 
     With respect to GPS-enabled devices, if GPS time is not available, and a sufficient amount of time has passed since the last synchronization such that NTP time would be considered more accurate than the device time, the device may attempt to synchronize itself to NTP time. The time synchronization method and device time at the time of the last successful synchronization attempt are stored in a computer chip memory on the device. Over time, the average accuracy of device time can be determined from this type of information. 
     A distributed time synchronization system and method are disclosed to dynamically synchronize a group of electronic devices to a common time base. As a group, electronic devices in proximity to each other can use point-to-point communications through the local network such as Wi-Fi or Bluetooth to “share” or otherwise update device time. The devices can communicate with each other to determine which device in the group has the most accurate time, and synchronize themselves with that device. The most accurate time, or a consensus time, may be determined using a number of factors, such as the elapsed time since the last synchronization, the method of synchronization, and average accuracy of the device. 
     Among a group of electronic devices in proximity to each other, such as in a room or other designated geographic area, there may be some devices which do not have GPS reception or Internet connectivity to get their device time updated. However, these devices can still communicate with each other using Wi-Fi, Bluetooth, or any other suitable network or local communication protocol. For example, a device near a window may have GPS reception, but a device further inside the meeting room may not. In another example, a device which had been recently carried outside and had its device time updated by a GPS signal may appear on the local Wi-Fi network. In these situations, devices in relatively close proximity may communicate with each other and determine which device in the group has the most accurate time. All electronic devices on that local network will then synchronize their device time to that of the most accurate device time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  shows a perspective view of a user wearing an analog display timepiece; 
         FIG. 2  shows a perspective view of a user wearing an digital display timepiece; 
         FIG. 3  shows a user electronic device receiving GPS and network signals; 
         FIG. 4  shows a perspective view of a mobile phone with time display; 
         FIG. 5  shows a perspective view of a laptop computer with time display; 
         FIG. 6  shows a perspective view of a computer tablet with time display 
         FIG. 7  shows a group of users with electronic devices in a network hotspot; and 
         FIG. 8  is a flow chart illustrating operations for time synchronization in one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. Like reference numerals denote like structure throughout each of the various Figures. Various embodiments are discussed below with reference to  FIGS. 1-8 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
     Referring to  FIG. 1 , a perspective view of an electronic device, which may be an electronic timepiece  11 , is worn on the wrist of a user  13 . Timepiece  11  includes a display  12  and a computer control device  10  which may control the content of display  12 . Display  12  includes a conventional analog clock face  14 , which includes an hour hand  15 , a minute hand  16  and a second hand  17 . User  13  may manually set the correct time by various means as is well known in the timekeeping arts. 
     Control device  10  may execute instructions and carry out operations associated with portable electronic devices as are described herein. Using instructions from device memory, controller  10  may regulate the reception and manipulation of input and output data between components of the electronic device. Controller  10  may be implemented in a computer chip or chips. Various architectures can be used for controller  10  such as microprocessors, ASIC and so forth. Controller  10  together with an operating system may execute computer code and manipulate data. The operating system may be a well-known system such as iOS, Windows, Unix, or a special purpose operating system or other systems as are known in the art. Control device  10  may include memory capability to store the operating system and data. Control device  10  may also include, or execute, application software to implement various functions associated with the portable electronic device or algorithms to embody a time synchronization system disclosed in various embodiments herein. 
     Referring to  FIG. 2 , user  13  is again depicted wearing an electronic timepiece  11 , which in includes display  12 . Timepiece  11  includes a computer control device  10 , which may be a computer chip that controls the content of display  12 . Display  12  includes a clock face  18  with a digital representation of the time as 11:42:17. As with the timepiece  11  shown in  FIG. 1 , this time may be manually adjusted by user  13  by various means as is well known in the timekeeping arts. That is user  13  may “set his/her watch.2” Generally, the embodiment of  FIG. 2  shows an analog clock face as opposed to a digital clock face as shown in  FIG. 1 . It should be appreciated that the analog clock face may nonetheless be controlled by digital circuitry and/or logic and embodiments described herein may be equally applicable to embodiments shown in  FIG. 1  and  FIG. 2 . 
     Referring to  FIG. 3 , user  13  is depicted wearing timepiece  11  in view of, or at least in communication with, a GPS satellite  19 . GPS satellite  19  is in orbit above the earth and may transmit a time signal  21 , which is received by timepiece  11 , and control device  10  updates the time displayed on display  12  based upon time signal  21 . That is, when user  13  is in view of satellite  19 , the timing signal  21  may be received by timepiece  11 . Being in “view” of satellite  19  generally means that the user&#39;s device may receive a signal from the GPS satellite or a device relaying such a signal. 
     When the timepiece  11  cannot receive the GPS signal, the time displayed on timepiece  11  may not be updated by time signal  21  from GPS satellite  19  and any drift of the timing device, which may be a quartz oscillator, may not be corrected. Timepiece  11  may also be in range of cellular tower  22  and receive cellular radio signal  23  that enables communication with other electronic devices through the cellular network. 
     Referring to  FIG. 4 , a perspective view of an electronic device, which may be a mobile phone, such as a smartphone  23 , held by user  13 . The smartphone  23  includes a display screen  24  which may include a touchscreen. The smartphone  23  may also include additional input controls such as an on/off button  25  and a home button  26  on a housing  27 . Smartphone  23  also includes a computer control device  10  which may be a computer chip that controls the content of display screen  24 . Display screen  24  may include a time display, which could be an analog display  14  or a digital display  28 . Both analog display  14  and digital display  28  are shown in  FIG. 4 . Displays  14  and/or  28  will show user  13  the device time as then known to smartphone  23 . As discussed above, this device time may be updated by various means such as a GPS time signal when smartphone  23  is located in an area with an unobstructed view of the sky such that time signal  21  from GPS satellite  19  may reach it. The smartphone  23  may also receive a Wi-Fi signal  22  through a cellular network or local hotspot as is known in the mobile telephone art. 
     Referring to  FIG. 5 , a perspective view of a laptop computer  29  is shown. Laptop computer  29  includes a display screen  31  and a keyboard  32  as well as user input devices such as mouse and controls  33 . Display screen  31  may include a time display, which could be an analog display  14  or a digital display  33  or both. Both analog display  14  and digital display  33  are shown in  FIG. 4 . Displays  14  and/or  33  will show user  13  the device time as then known to computer  29 . As discussed above, this device time may be updated by various means such as a GPS time signal when computer  29  is located in an area with an unobstructed view of the sky such that time signal  21  from GPS satellite  19  may reach it. Computer  29  also includes a computer control device  10  which may be a computer chip that controls the content of display screen  31 . Computer  29  may also receive a Wi-Fi signal  22  through a cellular network. 
     Referring to  FIG. 6 , a top view of a mobile computer or tablet  34  is shown. Tablet  34  includes a display screen  35  and user input devices such as a keyboard  36 . Display screen  35  may include a time display, which could be an analog display  14  or a digital display  37  or both. Both analog display  14  and digital display  37  are shown in  FIG. 6 . Displays  14  and/or  37  will show user  13  the device time as then known to tablet  34 . As discussed above, this device time may be updated by various means such as a GPS time signal when tablet  34  is located in an area with a communication path  21  from GPS satellite  19 . Tablet  34  may also receive a Wi-Fi signal  22  through a cellular network. Tablet  34  also includes a computer control device  10 , which may be a computer chip that controls the content of displays  14  and/or  37 . 
     Referring to  FIG. 7 , a group of users  13  is shown sitting around a meeting table  35  within a meeting room in a building (not shown). Users  13  may have a variety of electronic devices such as smartphones  23 , tablets  34 , timepieces  11 , and laptop computers  29 . Each of these devices may display the time in either analog or digital form as described above. Because users  13  and their associated electronic devices  23 ,  34 ,  11  and  29  are located in a meeting room within a building there is no access to timing signal  21  from GPS satellite  19 . Thus, the device time for each of electronic devices,  23 ,  34 ,  11  and  29  may not have been updated for some period of time and each of these devices may display different times depending upon their accuracy and the amount of time that has elapsed since the device time was last updated. In some situations, one or more users  13  may be sitting near a window and may have access to GPS time signal  21  while others in the room do not have such access and the device time from the device which has received GPS time signal  21  may be used as the synchronization time. 
     While electronic devices  23 ,  34 ,  11  and  29  may not have access to timing signal  21  from GPS satellite  19 , they may have access to a Wi-Fi signal  36  from a cellular network thorough a hotspot or other local area network device  37  which may be a router. While network device  37  is shown as located on table  35 , it can be appreciated that network device  37  is generally located out of sight in some other portion of the room or building. Some of devices  23 ,  34 , and  29  may also have Internet access through signal  36  and thus may have their device time updated to NTP time. As discussed above, NTP time is not as accurate as GPS time. The variation in device time among electronic devices  23 ,  34 ,  11  and  29  may, in some instances, not be significant. However, depending upon the amount of the variation, such differences may be distracting or may result in errors if precise synchronized time among users  13  is required to perform a time sensitive task. 
     Because GPS time is generally considered to be most accurate, it may be the preferred time to be used to update various devices through a shared communication link. However, if one of devices  23 ,  34 ,  11 , and  29  has been updated more recently with NTP or other time, the timing of the last update may weigh more heavily in determining the synchronization time. For example, if device  23  has been updated by GPS time three hours prior but device  29  was updated by NTP time five minutes prior, then the time from device  29  may be considered more accurate and be used as the synchronization time. 
     In one embodiment, the last user  13  entering meeting referred to in  FIG. 7  may be considered to be the most accurate because that device time may have been updated most recently. Thus, some embodiments may have devices updated with the time of the last device to enter communication with the others, or may weight this factor when evaluating which time to use as the basis for synchronization. Alternately, it may be determined that all times should be synchronized for convenience or for the orderly progress of a meeting and synchronizing to the last person to enter the meeting room facilitates this purpose. In another embodiment, the system determines which devices are in a predetermined group and time synchronization is permitted only for devices in that group. In another embodiment, the devices in a predetermined group may not be permitted to update time while in a group meeting (within geographic proximity) or for a certain predetermined period of time as during the pendency of a scheduled meeting. In another embodiment, a protocol could be employed in which a device requests a time update at certain time intervals or every device broadcasts its device time at certain time intervals and the scoring system determines the most accurate synchronization time from among those broadcast times. 
     Referring again to  FIG. 7 , users  13  may become distracted during a meeting if the device time displayed on laptop computer  29  is noticeably different from that displayed on computer tablet  34 . That is, user  13  sitting in front of tablet  34  may notice that the time displayed on laptop computer  29  in front of user  13  sitting next to her differs noticeably from the device time displayed on her tablet  34 . The embodiments described herein update each device time within the network such that the device times of each of a plurality of devices in a predetermined area are synchronized. As the meeting concludes and users leave the room to enter other network areas or hotspots, their updated device time may be more accurate and may then update the time on other devices. Thus, the most accurate device time may ripple through a building as users  13  move about the building or from building to building within various local area wireless networks. 
     While the discussion of electronic devices  11 ,  23 ,  34  and  29  has referred to their being updated by time signal  23  from GPS satellite  19 , it may be that some or all of these devices may not be able to sense timing signal  23  even if they are located in an area with a clear view of the sky and thus are able to receive signal  23 . That is, certain devices are not GPS enabled. As with the situation described above with respect to  FIG. 7 , it would be desirable to have time synchronization of all electronic devices within a defined area. In one embodiment, by using a local area network hotspot or Wi-Fi network signal such as signal  36 , all electronic devices within a predetermined geographic area may have their time display synchronized. 
     In one embodiment, to determine which of the device times displayed on various electronic devices should be used as the synchronization time, various factors are considered. For example, using the time from an electronic device that has been updated from a GPS time signal  21  may be one sample factor. That is, the origin of the time signal such as whether it is a GPS timing signal, an NTP time signal received via the internet, or even a manually input time change made by a user  13  may be a factor and this information may be utilized in selecting the most accurate device time for synchronization. A second important factor in selecting the most accurate synchronization device time is the amount of time that has elapsed since the device time was last updated. For example, while GPS time may be preferred, if the device time on one electronic device was last updated some number of hours previous by a GPS signal, but another electronic device time was updated by an NTP timing signal two minutes previous, it may be determined that the NTP signal is more accurate. 
     Another factor in selecting the most accurate device time from among a plurality of electronic devices may be the accuracy of the timing device itself. For example, if a timing device in a GPS enabled electronic device has been updated multiple times in a short time period, then that may be an indication that the quartz oscillator or other timing device may be inaccurate due to age, low battery power or other environmental factors. This inherent inaccuracy may be used as a weighing factor to determine whether the time on that device should be used as the synchronizing time. Similarly, if the device time, when checked against GPS signal time, has remained consistent with the GPS time, then that device time may be favored as the synchronized time. In one embodiment, the number of times that the device time has been updated in a prior predetermined period may be a factor in determining its accuracy for use as a synchronized time. For example, if a device has been updated by one second each week for the last 6 weeks when compared to GPS time, then it can be determined that the device time will be unreliable by some amount and this may be a weighing factor in determining its suitability for use as synchronization time. In another embodiment, if a device has not required a time synchronization because it has maintained its accuracy, it may not be required to check its device time as often as other devices. In addition, this more accurate device may be used as a more reliable indicator of the most accurate synchronization time when a scoring system is used for time synchronization of various devices. 
     The disclosed embodiments use distributed time synchronization to dynamically synchronize a group of electronic devices to a common time base. As a group, electronic devices in proximity to each other can use point-to-point communications through the local network such as Wi-Fi or Bluetooth to ‘share’ time. The devices can communicate with each other to determine which device in the group has the most accurate time, and synchronize themselves with that device. The ‘most accurate time’ may be determined using a number of factors, some of which may be the elapsed time since the last synchronization, the method of synchronization, and average accuracy of the device. The disclosed embodiments may be implemented in the electronic devices by software programming in control device  10 . Control device  10  may be programmed to consider weighing the above accuracy factors such as origin of the time signal and amount of elapsed time since the device time was last updated. 
     Similarly computer chip may be programmed to consider the accuracy of the crystal oscillator or other timing mechanism itself. Various triggers for updating the device time may also be programmed into control device  10 . For example, the device time could be updated whenever the device obtains a GPS time signal  21  as this is generally considered to be the most accurate time signal. The device could also be programmed to update periodically if no GPS signal has been obtained within a predetermined time. The device time could also be updated based upon entry into a new local area network or hotspot. The device could be updated based upon detecting a plurality of other devices such as when a user  13  enters a meeting room. The device time could be updated every time user  13  accesses his or her calendar. Some electronic devices may include sensors to detect vibrations or other motion of the device signifying that the user may be running and this activity may trigger time synchronization. Automobiles may be programmed to automatically connect a mobile phone to the car radio system via a Bluetooth connection when the automobile is started and this could trigger time synchronization in an electronic device. 
     The device could use a calendar as an updating mechanism. In one embodiment, the device time may be updated every morning at a certain time such as when the user awakens. In another embodiment, the device time could be updated at certain other times of the day such as every hour during a workday but less frequently or not at all in the evening. In another embodiment, an updating event could be triggered by the detection of a new network by the device. In another embodiment, devices may update or share time upon waking or receiving a signal (like from an accelerometer) that may correspond to a motion made to check time (raising wrist to look at watch, pulling phone from pocket such as an accelerometer detecting movement from a stationary position to motion across an arc). In another embodiment one device may initially set a device time before it polls others, a for example when a device is turned on or activated and it doesn&#39;t have time to receive a time update from other devices it may attempt to update its device time by accessing GPS or other available time standards. In another embodiment, the device may be programmed to synchronize its device time from another device after its screen blanks or it is put down. 
     Referring to  FIG. 8 , a flow chart illustrating one embodiment of a time synchronization method is disclosed. A triggering event prompts the electronic device to update its device time. The triggering event may be movement of the electronic device, entry into a new local area network, the passage of time, detection of adjacent electronic devices within a predetermined distance or other events such as detection of a GPS signal. In operation  38 , an electronic device receives a time signal from a GPS satellite. The electronic device has its device time updated. At operation  39  the electronic device is moved to a new local area network and is located within a predetermined proximity to at least one other electronic device. 
     At operation  41 , the control device  10  in electronic devices within the local area network of operation  39  are polled via a local area network to determine the origin of the last time synchronization of each device. At operation  42 , the electronic devices in the local area network of operation  39  are queried to determine the timing of the last time synchronization of each device. At operation  43 , a device time from one of the electronic devices is scored as the most accurate based upon operations  41  and operation  42 . That is, a scoring system may be implemented which includes a determination of the time since the last update of the device clock and what was the origin of that update (GPS, NTP etc.). The score could also factor in the inherent accuracy of the device, which, in one embodiment, could be determined by how frequently the device must be updated (i.e. the number of time updates in a certain time period in order to keep the device synchronized to GPS time). An algorithm programmed into controller  10  may implement the scoring system. At operation  44 , this device time is then selected as the most accurate time. At operation  45 , the most accurate device time from operation  44  is communicated to each of the other devices within the local area network and those devices update their respective device times to match the selected most accurate time. In an alternate embodiment, the communication of the most accurate time may be made from one device to another directly rather than broadcast to all devices in the area. 
     In embodiments where the current time of the electronic device is corrected, revised or otherwise changed to a shared or more accurate time, the device may also keep track of the original (e.g., unchanged) time. Some embodiments may revert to the original time after a period passes or an event occurs, such as the end of a scheduled meeting, a user setting the device to the original time or otherwise choosing the original time, reaching a certain destination (which may be detected by a position sensor such as the aforementioned GPS sensor), and so on. Certain embodiments may display both the original time and the shared time simultaneously. Likewise, some embodiments may only update a time upon a user&#39;s approval, either explicitly or implicitly (for example, through permitting or enabling such updating as a menu setting). 
     Further, certain embodiments may use the updates to a more accurate time to estimate a discrepancy between a device&#39;s internal time and the more accurate time. This estimation, optionally along with an estimation or measurement of a rate of change between the two, may be used to account for any error, drift or delay in the time measured and outputted by the device. As the device is updated more frequently through acceptance of a shared time, the estimation of both deviation from accurate time and a rate of change of the deviation may become more accurate, thus permitting the device to more accurately compensate for such error. This may permit the device to self-calibrate by leveraging the shared time obtained from more accurate devices or other sources, for example. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20140515
Publication Date: 20160531
Grant Date: 20160531
Priority Date: 20140515
Inventors: KING NICHOLAS V.
PRESTON DANIEL T.
KERR DUNCAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G04R20/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "G04G7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "G04R20/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04R20/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04R20/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04R20/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04R20/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04G7/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "G04R20/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04R20/26", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 56027805