Re: PSA: Clock drift and pkgin

> On Dec 13, 2023, at 4:52 PM, Mouse <[email protected]> wrote:
> 
>>> But a drift of a couple of % would not be unexpected.
>> Um, yes, it would be unexpected.
>> The crystal spec in that era was 0.01%, [...]
> 
>> If you see a couple % drift, that's definitely not the crystal.
> 
> I'm not so sure.
> 
> My experience is that older machines keep worse time than newer ones,
> even high-quality older machines and cheapo newer ones.  I suspect that
> crystal frequencies drift with time (or perhaps with something that
> tends to correlate positively with time, such as wide temperature
> ranges in storage).

Considering the physics of crystals and the specs of commercial ones,
it's hard to see how they would be much worse than 0.01% even long term.
Maybe FT-243 style, but those aren't used in computers.

> And, whatever the cause, I don't find a couple of percent drift
> surprising in practice.  I once had a machine (I forget what kind) that
> had really good timekeeping, just not at the frequency it was supposed
> to - exactly what I would expect if the crystal were something like
> 5-10 percent out of spec.

If I had such a machine I would definitely blame the software or
hardware for losing clock interrupts, and definitely not the clock
crystal.

Now, if I were looking at a PDP-11 -- which often uses the power line
frequency -- the question would be whether the modern power company
is doing a poor job on the power line frequency.  Apparently the
very tight specs they used to deliver in decades past are no longer
delivered.

	paul