Next message: Alexandre E Eremenko: "Re: Buying a sextant- a cautionary tale."
Alex E, you wrote:
"Probably, if I were on your place, I'd follow Frank's advise
and try to sell it on the same e-bay. (And recover at least a part of the
loss). "
That advice was in a test message to "NavList". I don't think GH has signed
up though most everyone else has.
And:
"But if you prefer to experiment with it
(which does not exclude the selling option!),
you may try to determine the index correction by carefully
observing star distances at say 10 or 15 degrees, where the arc is
usable, and then use it for the Lunars. But not for distances to
lighthouses."
Unless I mis-read his note, GH already got his money back from the seller
when he went to pick up the instrument. I was simply proposing a 'hypothetical'
and actually I assumed you would reply since that's exactly the problem
you've got, too, though on a smaller scale.
In a real sense, a table of arc errors is a table of index corrections as a
function of angle. The important difference from the standard index
correction is that arc error is not usually adjustable. So if you had a sextant like
this, if you adjust the index mirror, you would need to re-measure the arc
error at one specific angle. All the values at other angles should offset by the
same amount.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
