A 'simple' microcomputer is only the 'driver' of a crystal, and does not miscount or lose pulses. The accuracy of the clock is determined entirely by the crystal, and is typically accurate to about 6 parts per million without temperature stabilisation (5decC to 35degC) and substantially better with temperature stabilisation...about 1 part in 5 million. A 'buget' quartz based wrist watch (with stainless steel casing worn continuously) may exhibit a drift of less than half a second per month, or six seconds per annum. My diving chronometer which has a temperature sensor and some fancy software compensation has shown no significant drift ( better than 1 second) against the national broadcast time standard in the three years since I first set it. Quartz rocks! On Thu, Jan 3, 2013 at 10:13 PM, William "Chops" Westfield wrote: > > >> I see opinions that solar tracking doesn't need that much accuracy > > yes, but the usual behavior you get with a simple microcontroller > crystal-based timer is a continuous drift in one direction. If I did my > math right, a 1% inaccuracy in the timer makes your time be off by over 7 > hours after a month of operation, which is quite bad for solar tracking > purposes=85 > > BillW > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Perry Curling-Hope Research and Development --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .