Regarding the timing accuracy of using 32 Khz quartz xtals with
a PIC, typical 20 ppm xtal tolerance leads to a couple of seconds
of error per day. Somewhere I recall seeing where you can fine tune
this by using a variable capacitor, apparently at oscin.

Has anyone actually done measurements on the accuracy achieved using
this method?

Obviously, you have to also worry about xtal frequency wandering
with changes in temperature - order of 4 ppm with 10 degC, and 16
ppm with 20 degC change. The tuning cap will also wander.

I am wondering if is it really worth while going to the trouble to
try tuning these things - assuming the app will be in a situation
with normal daily temperature fluctuations - say at least 10-20 degC?

[let's assume for the sake of argument that no way are we ever
gonna use a temprature-controlled oven, etc - just let it hang
out come what may].

cheers,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
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