>
What home user even realizes they can change the clock time any more?Indeed. Even if you have the temerity to go and change the clock, the iPhone is secretly maintaining the true time internally and can use it or revert to it at will. I'm making a bold claim, so here are the steps to reproduce:
- Go to Settings -> General -> Date & Time -> Set Automatically -> disable
- set an incorrect time
- Go to Settings -> {Wi-Fi, Bluetooth, Cellular} -> Off
- Go to Settings -> Airplane Mode -> enable
- go someplace without any wifi or change the wifi password on your access point or
disconnect/power-off your access point
- remove the SIM card from the iPhone
- Now go back to Settings -> General -> Date & Time -> Set Automatically -> enable
- Surprise surprise! The date and time revert back to the correct value even though you have no possible network connection. How did it know the correct time?
Implementation thoughts: If the true time is 6:00pm and you change it to 9:00pm, the iPhone could calculate the offset as 3 hours and 0 minutes, and show you the time as 6:00pm + 3h = 9:00pm, but knows that the true time is really 6:00pm. The same effect could also be achieved by having two internal real time clocks (aka time of day clocks), one for the true time and one for the time you set.
My theory is that they'd prefer users not messing with the clock, but they provide a UI for setting your own time (such as for people who like setting their clocks 5 minutes ahead to never be late for meetings). However, they keep the true time for other purposes (perhaps for logging, syncing, or something else?).