In message <007c01c321fd$71891e80$6400a8c0@dell8100> Bob Ammerman wrote: > 31536000 seconds in a year. > 3 / 31536000 = 0.095 x 1E-6 > > In other words, you are looking for an accuracy of better than 0.1 part per > million. You are not going to get anywhere near that out of normal crystal > oscillators. Hmm... A few seconds +/- per month would be OK, but I still need to find a way to get the PIC to keep time accurately while it's at 4MHz. 99% of the time, the PIC will be running at 32kHz waiting for a keypress. Then when someone presses the power switch, it has to switch up to 4MHz, change the timing constants, calculate the hash and shut down again. I still can't see how to implement that ATM... Later. -- Phil. philpem@dsl.pipex.com http://www.philpem.dsl.pipex.com/ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.