Re: [PIC] 18F secondary oscillator by IVP .

> 10 secs in an hour, compared to the stopwatch on my phone Can you trust your phone ? Your ISR doesn't indicate anything that would cause such a large error, as far as jitter or latency is concerned anyway. 1/360 error is an odd sort of number for hex registers. If it was 14s (ie 1/256) then you might suspect a consistent high byte anomaly, for example the TMR1H loading. The datasheet recommends stopping the timer if it's asynchronous with the main ocillator before writing. Perhaps try that, with compensation for jitter, and see if that improves the accuracy, then look at the best solution. Possibly there's a timing mismatch between the s/w and the h/w, although if the main oscillator is running much faster than 32kHz that shouldn't be a problem Jo