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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brian Walton
Date: 2022 Sep 7, 22:02 -0700
It occurs frequently enough on a long voyage that the Moon and a planet are well separated at star time. If PLs from them cross tightly with any star on a well opposed azimuth, you can be sure with 3 shots, that your (mechanical) chronometer is well rated.
If you reduced these shots using a Bygrave replica, all calculations would have been done without any on-board use or knowledge of electrics, trigonometrical ratios, or logarithms. Plotting the St Hilaire PL would easily reveal the Sumner Line, time sight, and ex-meridian value should your master require them recorded in the deck log (!)
A "Chichester" procedure could eventually discover any chronometer error, again without any electronic aid, or other special trig formula.
You could practise this in your back yard. All we now need to live happily ever after, with power down, is for someone to produce written perpetual Moon tables. And nice weather.
Brian Walton
Sent just before star time
