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Thanks to Fred for his comments.

He wrote-

| Move the sentence on calculation precision to the end of this
| paragraph, to dovetail with the discussion of overall error.  This
| also sets up a discussion of the various methods of clearing, which
| all aimed to simplify the clearing process, hence Bowditch's claim to
| fame.

 I had intended to steer clear of any detail about various methods of
clearing, because that could be never-ending. Was I right?

And Fred has suggested the following insertion, the sentence starting
"Because"-

"...it
| > became a
| > severe test of a navigator's skill.  Because of the half-arc-minute
| > errors in both the moon's position predicted by almanacs and in the
| > measurement, great precision was required in the calculation of
| > Greenwich time.  The calculations, which were complex, called for
| > five-figure log tables of trig functions."

I disagree in detail with those words, Fred. It wasn't really the
imprecision of the observation or prediction that gave rise to that need for
precise calculation. More, it was due to that factor of 30, because of the
Moon's slow motion. The precision was needed in the clearing process, of
course.

George.

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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