[GTALUG] mysterious restarts

[James Knott]

On 06/19/2016 12:34 AM, Peter Renzland wrote:
>> > That's true over the short term, but long term accuracy is very good.
> Yes, because the power plant frequently advances and retards the frequency slightly so that the average is exactly 60Hz.
> That makes synchro clocks highly accurate.  IIRC, the German train station clocks are synchronized that way. (50Hz). 
>
>


There's more to synced clocks than just an accurate time base.  There
also has to be some means of setting them to the correct time.  These
days we have NTP.  For many years railways used telegraph lines to sync
clocks  Many years ago, ships in a harbour would wait for a noon cannon
to set their clocks.  In fact, the time base doesn't have to be all that
accurate, so long as the sync occurs often enough to keep the clock
accurate.