In sci.electronics.basics wrote:
Why do the battery powered clocks in personal computers tend to keep
worse time than quartz watches, even the $1 ones?

The computer batteries measure fine, at least 3.15V.

I thought that the problem was temperature swings in the computers
(25-38C), but a couple of cheapo watches taped inside the computers
kept better time.

The answers I found useful in the thread a
* Use internal capacitor to adjust for the crystal.
* Provide stable voltage.
* DS1387 (suns?) have a good track record.
* Crystal chassi shall be grounded.

Useing these facts it should be possible to construct a fairly precise clock.
A precise crystal with internal capacitor in shielded box powered by it's
own linear voltage regulator should do it?

It could then countup a synchronous counter on positive flank. And be read on
negative flank (and only then).

Regulator could use diodes to enable proper batteri/psu operation. Separate
regulator for counter and crystal.