bert wrote:
In article , Dave W
writes
On Mon, 22 Mar 2021 19:41:54 +0000, Scott
wrote:

On Mon, 22 Mar 2021 19:17:19 +0000 (GMT), charles
wrote:

In article ,
Scott wrote:
How does my car clock work? It cannot be quartz or radio controlled
as it runs slightly fast. It cannot be synchronous because the supply
is DC. Is there any form of adjustment to get it to run to time?

quartz can run fast - or slow,

In what circumstances? I thought it was supposed to be accurate to
one second in so many thousand years. Can the crystal be replaced?

Accuracy is what you pay for. I have had a few £1 rubber watches off
ebay, which either gain or lose 1 minute a day. Probably factory
rejects. So I bought a dozen crystals of specified accuracy for under
£2 the lot, which when installed in the watches rendered them decent
timekeepers.
My Rolex actually gains slightly - well they are clockwork after all.

There's a machine for adjusting clockwork ones.

The device here is digital and not quite the same.

https://diywatch.club/en/blog/how-to...-a-timegrapher

However, the output is made to look similar to the old one.
The old one used a chart recorder. If the chart pen drew
a straight line down the chart paper, the movement
was properly adjusted. If it went off on a
diagonal, to the left or right, it needed a bit
of tweaking. It's possible the chart recorder
version in the lab, had vacuum tubes in it.
I presume if the chart pen wiggled, it meant something
was worn and needed replacement.

I didn't try the machine out, but the guy in the lab said
some of the other staff used to come in and use the
machine for their watches. The machine was meant for
adjusting wind-up data recorders for the research ship.

For digital watches, I'm sure some crafty person would
attempt to make the output look like the timegrapher.
But a basic frequency counter would be all that was
really needed. And a frequency counter with a "good-enough"
reference inside. Not all frequency counters have good
reference oscillators inside. Some are just dreadful.
As long as they have the coax connector for 10MHz input,
you can connect an external reference. And then the
reference likely costs more than the frequency counter.

Paul