Measuring Clocks and Watches

Summary of the GPS Reference Receiver

  • Exceptionally accurate and stable
  • No cumulative error
  • Consistent phase relationship to clock
  • Vanishingly small errors

In summary, the beat time calculated by the computer from GPS referenced readings is much more accurate than the resolution of the standard timer. The significant characteristic of GPS measurements is that every reading is referenced to a precision reference pulse. Any imperfection in the precision of the timebase becomes insignificant. And as you measure for longer intervals, the error becomes a smaller and smaller fraction of the total measurement.

As an example, let’s suppose each reading has an error of plus or minus one microsecond. If you measure a one second clock beat, this is an accuracy of one part per million.

If you measure 30 beats with the GPS reference, the error in your reading is still one microsecond, but over an interval of 30 seconds. The measurement error of this reading is now just one part in 30 million.

If you measure for an hour, the error in your reading is just one part in 3.6 billion.


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