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    Re: Side error is not a real error
    From: Antoine Couëtte
    Date: 2021 Sep 28, 02:58 -0700

    Totally agree Frank.

    Thanks for addressing this. I have experienced it many times, although it is very seldom adequately covered in Nav Courses, and it possibly looks like one of the first times it is specifically adressed here on NavList.

    I have long preferred checking Sextant IE's directly through stars or even from a well defined horizon - when and if any - than through Mr Sun.

    Less risky to the eyes too.

    The best IE determinations I could and can ever make are from observing low altitude reasonably bright Stars (and if possible not planets because of their apparent SD's, unless there is sufficient daylight so as to make them look like "dots" and not small circles / patches of light).

    Hence at dawn and by 45°N I would preferably not shoot at Jupiter now (23.2" SD). I would rather choose Saturn (8.5" SD) which is about 20° to the West of Jupiter, but would definitely prefer shooting some bright star nearby (e.g. Antares still "usable" for a few more days).

    Simply trying exactly matching direct and reflected images while maintaining my sextant vertical.

    It does not matter, and it would rather even help, if I can see both images very close to one another. Just putting them "horizontal" while holding my sextant "vertical" and I can  immediately read IE. I am not advocating either accepting images wide apart, but up to one arc minute - or so - apart I have always considered it as a quite acceptable offset.

    After each set of observations, check again my IE, just in case it may have started drifting. 9 times out of 10, it won't, and it is certainly good practice to take this small extra half of minute of your time.

    And, by daylight or at dawn/dusk with a well defined and crisp/sharp horizon, I have quite a few times checked IE's directly from direct and reflected horizon images. Works fine too, but the best benchmarks for me remain low altitude stars. In other words, for me the Sun has always been my last resource checking source.

    On the other hand, when shooting Lunars, and by instinct I have always attempted to use a sextant with side error as small as possible, i.e. witouht accepting any visible side deviation.

    Antoine M. "Kermit" Couëtte


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