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From: Fred Hebard (no email)
Date: Mon Oct 06 2003 - 15:21:57 EDT
George,
Good post. I might note, however, that not all on this list are small
boat navigators. Some, indeed, are BIG ship navigators! Apparently,
they routinely can get their positions to under one mile, and even
under 0.2 miles. That is true also of land-based observers.
I found the quest to determine errors in my sextant to be useful in
motivating me to use the instrument enough to where I became proficient
with it. For me, the key element of proficiency in taking altitude
shots was accurate timing of the sight, while for measuring
interstellar angles, it was accuracy of measurement alone. There are
significant differences between the two. Ultimately, I chose to take
altitude sights since that is the common use of a sextant in navigation
today.
I don't think errors of 10-30" of arc could be detected by an observer,
but grosser errors, of over a minute, should be easily detectable from
land with an artificial horizon.
Fred
On Sunday, Oct 5, 2003, at 06:55 US/Eastern, George Huxtable wrote:
>
> Let's be realistic about all this: Sextants were designed to measure
> lunar
> distances, a measurement that demands (but seldom obtains) 30 times the
> accuracy of a normal altitude sight. That degree of accuracy is no
> longer
> needed, except for the "lunartics" among us. Except for such lunar
> observations, if your sextant can give you position lines within 3 or 4
> arc-minutes, that's as good as a small-boat sailor normally needs. And
> as
> much as a small boat sailor can usually expect, with the motion of a
> small
> craft in a turbulent sea.
>
> So should a small-craft navigator be worried if his sextant has no
> calibration certificate from its maker? I doubt it. It's almost
> certainly
> good enough for his needs. He should relax and enjoy using it - but
> always
> keep his eyes open for signs of any serious discrepancy, as applies to
> any
> instrument, new or old.
>
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