Hi TabSoft,

Possibly I am expecting too much from the internal OSC. The documentation states "Factory Calibrated to within+/- 1%"
1% of 24 Hours is +/- 14.4 minutes so my complaint regarding 2-4 minutes in 24 hours is well within the 1%

I took a look at the elap_timer include file and can't quite tell how I might make fine adjustments to the timing routine other than adding or subtracting in "Ticks" in the following code segment...
Code:
if Ticks = 200 then          ' Modified 04/03/2015 from 100 to 1000
                                  '  change Ticks = x to right interrupt time
                                  '  1000=1ms, 100=10ms, 10=100ms, etc.
Ticks = 0
Am I on the right track??

Is it the case that this include file is somehow self calibrating??
If so how does that happen? and against what standard?

This is all somewhat low priority as it is just for a real time clock that only displays hours:minutes and I can opt to check NTP time (more than once a day) or go to an external crystal oscillator.

Thanks for any guidance or explanation you (or others) might be able to offer.