6v6gt:
Since that original design, there are a number of methods of getting an accurate time signal to update a clock:
- Global positioning system (GPS)
- Network Time Protocol (NTP) either over ethernet or Wireless Lan
- Long Wave Radio Time signal eg DCF77 Europe or equivalent in USA (WWVB etc.)
But, all have some disadvantage: poor indoor reception or set up configuration required or cable connection required.
However, the chips to for autonomous operation of clocks are now cheap and accurate eg. DS3231 with inbuilt crystal ageing compensation.
That is all true but I sell replacement clocks for legacy systems. We correct for schemes form the 1950's. Also most sync clock systems are less concerned with having the correct time than the SAME time. If you use a 'cloud' time and attendance system they most definitely do not use NIST time, so the client can set the master to the same time as the TA cloud and the wall clocks will agree with the TA system.