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    Re: Hints2Travellers 1883: graphical LD clearing?
    From: Tony Oz
    Date: 2022 May 12, 00:45 -0700

    Frank, Herman, thanks for the replies.

    First of all - I was surprized to learn that graphical LD clearing methods existed.

    Yes, I understand that its' claimed one-arc-second accuracy was limited to that particular example they worked upon, also they warn that LDs over 90° are not for this method.
    Regarding the magical divisors - yes, they look suspiciously similar to the Moon's HP boundaries.

    Hope Lars could shed some light into this graphical construction.

    By the way, the following pages (p087~p090) discuss an "equipmentless" latitude determination, there too is some graphical - stereographic - solution to the problem. Very interesting, because I met a more advanced implementation where a pair of stars may be on the same almucantar. Having observed such pairs - on the same vertical or on the same altitude - one gets a fix. This is similar to the Weem's plots of altitudes' isolines. (The article is in Russian but the formulas and the drawing must put the idea clearly)

    Warm regards,
    60°N 30°E

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