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From: George Huxtable (no email)
Date: Mon Oct 06 2003 - 20:30:49 EDT
I agree with much of Fred Hebard's recent posting, but with a few quibbles.
>...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.
I concur with the one-mile figure, but would be reluctant to accept the
claim of any big-ship navigator to routinely achieve positions within 0.2
miles. This might be achieved on occasion, however, but only by lucky
accident. Anomalous-dip errors, alone, are likely to exceed 0.2 miles.
>That is true also of land-based observers.
A land-based observer using a good liquid reflector is much better off than
the mariner, because his observations don't involve the horizon, and
because his errors (with his sextant readings) will be halved.
>
>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.
For checking sextant calibrations, using the altitude of a body near the
meridian can bypass the need for accurate timing.
>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.
I certainly agree with Fred's view here..
George.
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contact George Huxtable by email at , by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
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