Thanks for AN590 in my quest to build/program a accurate clock.  It did
help a lot, however my technique is a bit different from the APP NOTE.

 I am using a 32 KHz crystal with the prescaler dividing by 16 and the
RTCC rollover interrupt every 256 cycles.  This gives me (or is suppose
to give me) a interrupt every 2 seconds.  I then use a counter to roll
over ever 2nd interrupt and there I have my timer!

I ran it last night and the next morning it was late with about 1/4
second.

Can anybody tell me why?
 Is is possible the the crystal freq. can change with the apply voltage,
the voltage I used was 2.5V.



Thank you

Louis Botha