Nick Sayer writes:
> The WU standard time service goes back further than the turn of the 20th 
> century. It started in 1870.

See also: http://leapsecond.com/history/usno.htm

> I’ve always wanted to get my hands on one of those clocks and come up with a 
> circuit to recreate
> the synchronization signal for it, probably with a Raspberry Pi running ntpd 
> and a big ol’ MOSFET.
> The problem is that at this point, those clocks are quite expensive once 
> they’re reconditioned.

You will find lots of these auto-setting self-winding clocks on eBay. Some are 
very reasonably priced.

There's a bunch of clock guys out there who play with these and you'll find 
circuits and information with a google search for words like self-winding clock 
company or SWCC or Western Union USNO and so on. Start with:

https://en.wikipedia.org/wiki/Self_Winding_Clock_Company
http://www.telechron.com/swcc/swcc.html
http://www.kensclockclinic.com/pdf/PoweringSWC.pdf
http://community.nawcc.org/chapter52/pages/selfwindingclockco

Mitch's (www.telechron.com) and Ken's (www.kensclockclinic.com) sites are 
superb.
 
Also, for a screen full of irresistible SWCC photos, try this:
https://www.google.com/search?tbm=isch&q=self-winding+clock+company

> My understanding (perhaps incorrect) was that the sync pulse was once daily 
> and, as you said,
> would cause the hands to “snap” to 12. The trailing edge of the pulse was 
> synchronized and would
> release the clock to operate normally.
>
> That they had something as accurate and widespread as it was so early is 
> astonishing.

Oh, Padawan, that's just the tip of the iceberg when it comes to the deep and 
fascinating history of precise timekeeping.

/tvb
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