NavList:

Thank you for your suggestion, but sorry Frank, but I am now fully happy with the assessments I have made and conclude it is near impossible to obtain better sights than around one minute of arc (plus or minus 1/2 moa) generally and easily for Lunar distance measurements - which resolves to a time indication of no better than two minutes in time.

...and that for Moon Jupiter measurements I have been testing, where Jupiter is like a lighthouse beacon in the sky, and the relative movement of Moon/Jupiter is over 31 minutes of arc per hour - as it is just now.

I accept it might be possible with care and experience to better this perhaps by a factor of two, but it is certainly not easy; and I can't do it.

In fact I have just gone out right now and obtained a sight with a 2min-29" error (1 and 1/4 moa error) for Moon/Jupiter at 20Hr-51min GMT on Sunday 24th Oct 2010.
The variation I obtain can be as much as + or - six minutes of time out - three minutes of arc.

Nearly all of the tests I have done whether with my 'best' sextant or even as I have included - a box sextant, are no better (mostly) than within + or- four minutes of time, equivalent to two minute of arc. If I am near two minutes of time - one minute of arc I feel I am doing well.
It seems a standard deviation of around one and a half minute is the best one can expect in normal practice.
Your suggestions of measurements better than this to consistently sub-minute accuracy I do not obtain and (forgive the pun) frankly, doubt it possible.

We shall have to agree to disagree.

Douglas Denny
Chichester. England.
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