Just to remove your uncertainty: a wall clock second is a common ordinary second. The warnings about the inaccuracy
of alarm are due to resolution.
It would be similar to you trying to time something
with a digital watch that reads only to seconds.
You cannot tell where you are in the current second, so
your accuracy can be off by nearly a second.
Comment on Re: Tk related -- timed event and $SIG{ALRM}
Hmm. Ok. I did some more testing and I learned that if I wasn't doing something with the running script ie moving the mouse over the window, clicking buttons, etc then the ALRM never triggered. This was one of the reasons I associated the wallclock seconds with clock cycles associated with the application vs general clock cycles.