pito:
Wristwatch is Wrist watch. The temperature range should be ~37°C and not 0°C to +40°C.
The 32kHz tuning fork crystal for watches has been chosen as a compromise of size and the fact it has a most stable region at 25-28degC, what is a typical temperature at your wrist. The ratio of wearing the watches on the wrist, afaik, is 16h/8h. So the watches crystal frequency is set. I have got a cheap kitchen clock with 4.194M crystal and it does a few seconds a year (!), what is a matter of luck, of course. Pls consider the capacitance used with the crystal as well, as it has a huge effect. For example a 1-2 pF change with a 32kHz watch crystal makes few seconds a day.
PS: pls mind the terms "stability", "precision" and "accuracy" are tricky when talking timekeeping
A clock might be perfectly precise but inaccurate..
http://literature.agilent.com/litweb/pdf/5965-7984E.pdf
Nice article. I particularly liked this paragraph:
The most accurate measurement known to humanity is the measure-
ment of the duration of the second. The peak of the pyramid for accu-
rate time and frequency is the international reference, UTC. The current
best accuracy for the determination of the second results in a time error
of ±0.3 nanoseconds (billionths of a second) per day. This is equivalent
to ±1 second in 10 million years.
As the article may be somewhat dated the current time error may be even less?
Lefty