I'm recording data from three different phones, one from iPhone (blue line) and the other two from Android devices. The phones are fixed on a board and the board is being being hit a few times to check the synchronization. While I don't expect that the events (board hit) are recorded at the same time (different internal times of the phones) I do expect that the interval between the events should be the same. However, while the events recorded by the Android devices show the same consistent delay, the same does not happen for the iPhone. It looks like the delay is increasing with time, as can be seen from the attached plot.
Does anybody have an idea why?
Thanks in advance.