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    Re: Index correction sun sights
    From: Alan S
    Date: 2012 Feb 20, 13:21 -0800

    Randall:

    For whatever it might be worth, based on what I've been told by people who know better, as well as what I've read of sextant manuals, the following might be of interest.

    Those mirror adjustment screws should be turned as seldom as possible. Respecting index error, unless it gets to be something outrageous, check index error at the start and again at the end of a series of shots, and average the results, using that number as the index error correction. Fiddling with adjustment introduces wear to plastic sextants one is better off without.

    Like you, I'm a landlocked navigator, I find celestial navigation an interesting pass time, something to do when I get to the beach, or in Pittsburgh "down to the Mon", unless I break out an AH, and shoot in the parking area of our apartment complex.

    With a Davis Mk. 15, I use the above described approach. With a metal frame sextant, an Astra 111B, I check index error whenever I shoot, and usually take the average of 2 readings. Otherwise I might adjust mirrors once a year. With the Astra sextant, index errors are small, perhaps a couple of minutes or less, most always “on” the arc, at least so it is with mine.

    Alan

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