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© Copyright 1999, Jim Loy
I see that you can now buy a digital clock, which gets its time from the atomic clock at the National Bureau of Standards, in Denver, Colorado, by radio. It is nice to know the time that accurately, I suppose. Most of us adjust our clocks to work time, or TV time. We keep our clocks accurate, by adjusting them every time that we notice they are in error. This works pretty well.
Your regular wrist watch, one with a second hand, essentially counts oscillations in a little wheel that rocks back and forth. This is pretty accurate, but must be adjusted every once in a while. Your grandfather clock counts swings of the pendulum. This is accurate, but must be adjusted every once in a while. Your digital watch is pretty accurate. It is counting electronic oscillations in a quartz crystal. This also must be adjusted every once in a while.
Most digital clocks which plug into a wall socket are perfectly accurate, over a period of time. What those clocks are doing is counting the cycles of your 60 cycle (50 cycle in Europe) electric power. "That cannot be very accurate," you say, "that depends how fast the power company's generators are turning." But, the power company keeps this electricity at a fairly accurate 60 cycles (60 hertz). And, here is the amazing part, they adjust the speed to make up for past inaccuracies. If they were slow in the past, they speed it up, so that the total number of cycles (over weeks or months) is the exact, right number. They do the same thing if they were fast in the past. So, over a period of time, your digital clock is probably perfectly accurate.