I recently added a time output to my script - it counts up how long it has been running - so every minute it will output something like this:
00:00:00 ... message ... 00:01:00 ... message ... 00:02:00 ... message ...
and so on.
I found that even after the board has been powered up for a long time, if I open the serial monitor and check the output, I see 00:00:00 !
Yet, the program should be running even if the serial port is open?