NavList:

   

Reply

Red has written, about the zeroing gimmick sold with Plath sextants-

| But failing to use the device, which can and often will eliminate
one potential
| source of math error from your reductions, makes absolutely no sense
at all. It
| would be what I call "belligerent ignorance", taking pride in NOT
obtaining or
| using the information and resources that in this case are literally
at your
| fingertips.

Red can call it what he wishes. He seems determined to pick an
argument, where none really exists. That's all right. I've done the
same myself, many a time, though it's an urge than nowadays I do my
best to control; not always with success.

If Red distrusts his own arithmetic, to the extent that he lacks
confidence in adding or subtracting the odd minute, or fraction
thereof, in his head or on paper, then he may have a special problem.
He is welcome to use that gimmick to avoid it, and I have not said
anything contrary, if he reads what I actually wrote. But if his
arithmetic is that untrustworthy, he is going to have difficulty at
the next step, correcting for dip, refraction, semidiameter.

On a slightly different matter, something else Red has said worries me
somewhat.

He wrote-|
| While you've got a sextant in your hands for the first time, and
presumably you
| are taking the time to check it for errors and adjust them out...

and in an earlier message-
"But it is something that a
user certainly would do the first time they got the sextant, and were
trying to
set up a baseline of adjustments on it, including the mirror
positions."

Well, that might be a reasonable attitude if a sextant arrives
secondhand, with an unknown history from another owner. But I get the
picture, rightly or wrongly, that if a sextant arrives new from its
maker, properly packed in its undamaged box, Red is itching to get out
the adjusting tool and tweak whatever he can get at. Such an
instrument has presumably been adjusted at the factory, at least as
well as it ever will be thereafter. What on earth does "set up a
baseline of adjustments" mean?

Red is perfectly welcome to tweak it as he wishes; it's his sextant,
after all. A better policy, in such circumstances with a new
instrument, might be to carefully check over all the relevant points
(perpendicularity, side error, collimation), but most users would then
be better advised to keep their hands off the adjustments, unless a
serious error shows up. And if it does, in those circumstances, I
would expect the maker to want to know about it.

Yes, all sorts of adjustments are provided, to allow for correction
for any events that occur in a sextant's life. And the maker properly
provides an explanation of how to check the sextant and make those
adjustments, if and when they become necessary. But that is not an
invitation to get twiddling straight away, even if the new owner is a
chap who enjoys doing so.

Judging entirely by what he has written, Red appears to put himself
into the category of a "sextant-worrier". Novice owners would be
well-advised not to follow that path. I would be rather careful, about
any instrument that has been in his possession.

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.

   

Reply