Celestial Navigation · Time — Watch Error
You time a sight by a comparing watch that is 00m 06s fast on the chronometer, and the chronometer error is 00m 12s slow on GMT. To get GMT of the sight you:
- ASubtract the watch's 6s fast, then add the chronometer's 12s slow, to the watch time✓ Correct
- BAdd both errors to the watch time
- CSubtract both errors from the watch time
- DIgnore the watch error and use chronometer time only
Explanation
Reduce watch time to chronometer time by removing the watch's fast error (subtract 6s), then apply the chronometer error to get GMT (slow chronometer reads low, so add 12s). Careful bookkeeping of fast/slow signs prevents a timing error that shifts the longitude.
Authority: Bowditch (Pub. No. 9), comparing watch and chronometer error
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