NavList:

Andrew,

I don't know how to say it any differently from before:

"If by the sun dial it is 12:00:05 at this moment, the sun must have passed the meridian 5 seconds ago, so that would have been at 11:59:55 mean time."

Your problem might be that you don't appreciate what it means to add these 5 seconds: Namely, you are converting mean time to apparent time. This is the time that a super accurate sundial would show and, of course, indirectly, also your sextant. But knowing apparent time in and by itself is pretty useless because all your watches show mean time. So the real question is not "How late is it on a sundial at 12:00:00 mean time, but the question is "What mean time will my watch show when the sun is in meridian transit. The sun is in transit at 12:00:00 apparent time. So, if the almanac tells us that we have to add 5s to mean time to get apparent, then we have to subtract 5s from apparent to obtain mean.

Herbert
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