In message  <246B76F30FF@its-eng1.eng.monash.edu.au> PICLIST@MITVMA.MIT.EDU
 writes:
> On previous experience, crystals do not give a good time base for a
> clock as the frequency varies quite a bit with temperature. I can get
> +/- five or ten minute error over 1 day. The mains is reasonably
> accurate for this purpose. ( Most commercial clocks rely on this fact.)

Hmmm.

My (very inexpensive) watch uses a crystal and doesn't seem to loose
or gain time at all. Checked against the radio daily. Also, the crystal
clock in my car (which is subject to some fairly large temp varyiations)
keeps time remarkably well.

In the UK, there is a specification that the number of cycles delivered
in a 24 hour period is kept constant, but the variation within that
period can be as much as 10%.  I can't imagine a crystal varying
that much.


Regards,


Mike Watson