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I have changed the threadname to make it more relevant.

Once again, Frank Reed makes flippant excuses to avoid tackling a specific
question.

Frank Reed would like to think that my disbelief in his claimed accuracy in
determining longitude around noon is due to my "confusion". Let me assure
him, once again,  that there is no confusion in my mind or in my postings,
on that topic. I simply do not believe his claims.

Of course, he or I can think up scenarios in which his claim of "1 mile in
latitude, 5 miles in longitude", can indeed apply. However, he has insisted
that it also applies to such "hard cases" as, specifically, that Winter
approach to the Clyde. And yet, when challenged about the hard numerical
details, the result is evasion.

Well, it's up to him. If he wishes to convince sceptics (and there are more
than just me) then he will have to respond to sceptical questions. Assertion
and reiteration do not make a convincing argument. If he insists on
selecting his own test-ground, that won't persuade doubters.

So here, again, is that simple question, as yet unanswered-

Take the example that I suggested, a vessel approaching the Clyde in
midwinter, in latitude 56 degrees. Her navigator spends 40 minutes on the
bridge, around noon, measuring altitudes of the Sun to determine his
longitude. Given that his sextant altitudes are precise enough to determine
latitude to 1 mile, just how good are they required to be to determine his
longitude to within 5 miles, as Frank claims he can? A complete error-budget
is requested, with due allowance made for any errors in ship's speed and
course through the water and rate and direction of tidal set, stating the
precision with which they need to be known.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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