On Tue, 21 Mar 2006 07:39:50 -0500, Spehro Pefhany wrote:

Here's the data sheet for a typical tuning-fork style watch crystal:
http://www.ecsxtal.com/pdf/ecs-3x8.pdf

Initial tolerance +/-20ppm, typically changing only about -5ppm for a
+/-10°C change (centered around 25°C).


If you carry it around on your wrist most of the time (I have a leather
band and I only take it off for showers/pools/etc), the temperature
is stable to within 1°C or so: 0.5 ppm is approx. 1 sec / month.
I actually see something like that on my $35 Timex.