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George:

 

Thanks for enlightening me. But I'm a bit hazy about your reference to error and rate. I think of error as the total change, and rate as the daily change. If the rate is known, than the error can be calculated, and therefore eliminated. I note that Cook's chronometer had a quite constant rate between mid-1773 and mid-1775. Knowing that the rate of change was constant, he could have made corrections based on elapsed time from the last calibration. I assume that was the normal practice to minimize uncertainty.

 

I just consulted Bowditch, who defines chronometer error as The amount by which chronometer time differs from the correct time to which it was set, usually Greenwich mean time. Chronometer rate is The amount gained or lost by a chronometer in unit time, usually seconds per day. I earlier referred to his definition of a chronometer as a timepiece with a nearly constant rate.

 

On my first visit to the Greenwich museum many years ago, I spent the whole time examining John Harrison's chronometers. The H1 instrument was working then, in its glass cage. Really amazing! I was surprised, and just presumed that periodic maintenance must have been applied. I'm with you in hoping that it will be restored to working order again, although it may be just a matter of time (no pun intended) before the next weakest link expires.

 

Jim Wilson