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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: "A diagram of C23 basic types"
Date: Thu, 17 Apr 2025 17:56:29 +0200
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On 16/04/2025 02:53, James Kuyper wrote:
> On 4/15/25 18:56, Keith Thompson wrote:
> ...
>> The uncertainty in the timing of January 1, 1970, where 1970 is a
>> year number in the current almost universally accepted Gregorian
>> calendar, is essentially zero.
> 
> Modern Cesium clock are accurate to about 1 ns/day.That's an effect
> large enough that we can measure it, but cannot correct for it. We know
> that the clocks disagree with each other, but the closest we can do to
> correcting for that instability is to average over 450 different clock;
> the average is 10 times more stable than the individual clocks.
> 
> Note: the precision of cesium clocks has improved log-linearly since the
> 1950s. They're 6 orders of magnitude better in 2008 than they were in
> 1950. Who knows how much longer that will continue to be true?
> 

I don't think cesium is still the current standard for the highest 
precision atomic clocks.  But anyway, the newest breakthrough is thorium 
nuclear clocks, which IIRC are 5 orders of magnitude more stable than 
cesium clocks.  (And probably 5 orders of magnitude more expensive...)

>> ...  Same for any other less commonly
>> used chosen epoch.  The fact that the number 1970 is arbitrary
>> is not a problem for software.  In fact it's an advantage, since
>> there's no uncertainty in the presence of any new information.
> 
> I agree, which is why I identified that epoch as the one I preferred
> over both of those.