What is the Frequency Error of a good Clock?
I’m not sure, but but I think a chronometer is allowed to drift mostly by six seconds a day when the temperature doesn’t change by more than 15 Celsius from room temperature. That corresponds to a frequency error of 69 PPM. I read about a temperature compensated quartz that should guarantee a clock error of less than 15 seconds per year, but I think they were actually talking about the frequency variation instead of absolute frequency error. In any case that would be 0.47 PPM. As I actually own a wrist watch that should include that quartz, I can state that the absolute frequency error is about 2.78 PPM, or 6 seconds in 25 days.
