3 ms·

I assume all mission-critical clocks get their tick from a quartz crystal. Clocks running on mains frequency is a very cheap cost cutting measure.

• Piskvorrr 9y ago
  If your clock is mission-critical, it should be rather well kept. Quartz, NTP, GPS, the list goes on and multiplies like rabbits (redundant this redundantly connected to redundant thats and backed up by those...). But indeed, sometimes you don't need sub-second precision, and relying on The Grid is useful.
  • blattimwind 9y ago
    I only have some experience with lab clock sources, but even those have some amount of redundancy by nature. They are generally a very good oscillator (e.g. a very good OCXO) disciplined to a reference with much better long-term deviation (e.g. DCF77 [uses a PM carrier, not the timing signal], GPS, a rubidium source or a miniature caesium source). Short-term (minutes to hours) is governed by the oscillator, and all these sources will enter holdover when the reference does something stupid. More recent ones can tell you the error margin during holdover. Distribution amps can have redundant and cross-checked inputs for independent sources.
• chx 9y ago
  If it's mission critical then -- in Europe -- it gets the time from DCF77. It uses an atomic clock to emit a time signal (actually, it uses three and only uses their output when two out of three agrees). It is also compared to further atomic clocks and corrected as necessary. Even many consumer grade clocks will sync to the radio signal once a day and use a quartz otherwise.
  • detuur 9y ago
    I suppose that in the case where the mission itself is critical as well, then indeed it's going to have an atomic clock signal.