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    Re: Reliable Index Correction to a Tenth Minute of Arc; WAS Longitude by lunar altitudes
    From: Antoine Couëtte
    Date: 2010 Feb 17, 07:35 -0800

    Frank,

    While we are at sextant index corrections, I will be most interested at reading your method.

    You certainly earlier adressed it in Navlist, as you seem to imply, but unfortunately I certainly missed it too !

    As far as I am concerned, the way I always used to get a consistent and quick index correction was (at dawn or dust only) to look for a rather faint star next to the horizon, keep the sextant vertical and align both images and read the index then. I would guess - or at least, this is what I have found - that the result is most generally, if not always, very accurate, consistent, quick and reliable.

    Obviously you need a well calibrated sextant with the 2 images extremely close to one another at minimum distance. I also have observed that when the images do not exactly cover one another, it does not really matter as regards the final result and it is even easier to best appreciate when both are "horizontal". But I also have to confess that I have had the extreme luck of an super-sharp eyesight, very useful earlier as a fighter pilot, still very much apreciated nowadays for sextant shooting, and even funny when in a group of friends for far distance acquisition of (feminine) target(s) for example :-))

    I will certainly read your method with a lot of attention,

    Thank you again in advance and

    Best Regards

    Antoine


    Antoine M. "Kermit" Couëtte
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