>>Keeping accurate time is a job for a Metrology Engineer, which was my previous profession. We could measure time to an accuracy of plus or minus 1 second in about 20 million years. What is important is we did not have to wait too long for the results. 20 million years can be a long time.
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>HP cesium beam by any chance? Have I got a story...

Jim;

Yes. Tell me your story and I will tell you about GPS and Trimble Navigation.

Tom