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Re: Sextant accuracy with short distance to horizon
From: Michael Wescott
Date: 2001 Jun 22, 12:56 PM
From: Michael Wescott
Date: 2001 Jun 22, 12:56 PM
> Later we did the noon shot and his results were about 68 miles off for a
> bunch of shots. These were taken in Guemes channel with a local horizon
> less than a mile away.
As others have pointed out, there is a calculation/table for Dip
when the sight is taken against a point that's closer (below) the
visible horizon. And the error will be toward, so you should've
calculated a position further south than you really were.
But an error of 68' is too much. That implies a shore line closer
than a tenth of a mile; about 170 yards if He is 10'. If you were
that close, it explains the error.
I think a good guess at the bulk of the error was a mis-reading
of the sextant by a degree. Personally, I find that one of the
easier errors to make, especially when the drum reads in the 50's.
Off by a degree and the error reduces to about 8' which is quite
reasonable considering the record from earlier in the day and the
Dip-short situation.
--
Mike Wescott
Wescott_Mike@EMC.COM
