Sorry Peter...I just found the replies to my send. To answer your Q's: >Umm, that's about 150ppm. Is this in a temperature controlled environment ? Like a basement lab underneath an inhabited house ? Yes. It was at my desk at work, and I only sampled the accuracy during the day. AC temp ranges probably < 5 degF. My supply is using a 7805 0.1W regulator and Imax is ~30mA. It's possible there is some hourly variance in the supply, based on # of LED's on (range from ~10mA to ~30mA for 3 LED's to 9 LEDs, each at ~3.5mA with a 50% duty cycle while on) but I would expect the supply to be good and temperature to be more of an influence on accuracy. This may be a false assumption. ?? Interesting also, was that my observations over 1 week showed that when the variance occured (positive and negative), it was a slow drift and return (about 5-10 seconds per hour). This could be due to supply or temp.... >RC clock drift is hard to find in the Microchip docs. AN588 is too old to be useful I think. More details: Using the internal 48Khz osc., I have a seconds counter for my ISR, and main takes care of all the updates. My loop counts are: 66 on TMR0 counter, 202 for outter loop second-counter. With 8 instruction cycles for my ISR ( 13 total ISR inst. cycles - 2 for TMR0 reload - 6 for counts after TM0 reload within ISR + 3 cycle latency), that should put the internal osc at 14948Hz ( (66+8)*202 ). Well...those counts ended up working, as anything less was too fast, and anything more was too slow. But with drift it may be hard to tell. The device specs show fairly good accuracy, and I spent about 2 weeks adjusting my counters for more precise short term accuracy. I was happy to see the long term accuracy was good, and being within 1 second after 5 days is good enough for me. Hmm...I may be calculating something wrong based on my ISR latency and TMR0 reload though...since it should be around 12Khz. ?? __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist