[apaprocki]

If I'm reading the spec sheets correctly, the datacenter rubidium/gps clocks typically used advertise < 5x10^-9 (worst case) to < 5x10^-11 (best case) accuracy.

[dclusin]

Which spec sheet? Would like to read more about these.

[apaprocki]

Something like this:

http://www.spectracomcorp.com/Desktopmodules/Bring2Mind/DMX/...

The units are a bit confusing but the accuracy still translates down to a handful of nanoseconds per month, I believe.