On Wed, Jun 15, 2016 at 3:46 PM, Stewart C. Russell via talk <talk@gtalug.org> wrote:

If you're lucky enough to get a tour of the IESO's HQ, they have a relic
of the 25 Hz era on the wall. It's the display clock from the Shortt
Synchronome pendulum clock they used to use to regulate the grid.
Synchronomes are the most accurate mechanical clock ever made, and one
has even been used (briefly, ill-advisedly) as an NTP server.

Now that is a lovely piece of timekeeping. Elegantly simple, and 2.3ppb??! That's a remarkable achievement for any clock from any era, let alone almost 100 years ago. Your average quartz oscillator is five hundred times *less* precise.

With that kind of medium-term stability, it could probably be used to discipline a quartz-based clock (with requisite filtering) to generate quite respectable NTP service.