[LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?

[Hal Murray]

phk at phk.freebsd.dk said:

> It used to be pretty good, because people used synchronous motors to drive

> clocks so the power companies tried to keep the long-term frequency correct.


Microwave ovens still use the line for timekeeping.  1/2 :)

I wonder how many old mechanical (synchronous) clocks are still "ticking"?   
I have two.  One on a clock radio and one on my oven.



> In Denmark they usually lost a couple of seconds during the day and gained

> them back during the night, similarly they lost half a minute over winter

> and gained it back over summer.


Do you have data or references for that?  If I heard it from anybody less 
credible, I'd guess it was an urban legend?  Was it accurate 50 years ago?

The winter/summer variation doesn't make sense to me.  If the PLL can cover 
daily changes, anything lower frequency would be covered for free.

It's easy to collect data.  Take an AC wall wart type transformer and connect 
it to a modem control pin that the kernel is setup to use for NTP's PPS 
signals.  (Contact me off list if you want the software.)

I have data from Silicon Valley and Zurich.  I can't see any strong daily 
cycles.  Some days are flat, some days it drifts one way, and some days it 
drifts the other.  Mostly it wanders around.  Typical peak-peak (SV) is 4 
seconds per day.  Here is a graph for the last 24 days:
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/Dec-2013.png
Midnight UTC is 4 PM local.  Peak-to-peak over 24 days is 12 seconds.


> After deregulation nobody gets paid to keep the long term frequency, so

> mains is no good, actually down-right bad, for timekeeping anymore. 


At least in the US, the power companies are still required to keep good time. 
 I don't know any details.

There was a proposal a year or so ago to drop that.  I gather it's a 
pain-in-the-ass type constraint on their overall operations.  The proposal 
was dropped and I haven't heard anything since.  Maybe somebody told them 
that microwave ovens have replaced synchronous
motors.  Maybe somebody figured out that it was cheaper to pay a few engineers to get things right rather than pay dozens of lawyers to get their proposal through Washington.

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This is getting off topic for leap-seconds, but maybe there are some details from the power industry that will shed some light on the leap-second issues.



-- 
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