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    Re: Emergency navigation: a Nocturnal as the Local Siderial Time source.
    From: Francis Upchurch
    Date: 2016 Sep 2, 01:09 -0700

    Hi Tony,

    I think Frank has already answered your questions better than I could have done.

    My new enlarged version of the Nocturnal is on the boat but I'll get some photos and send next week.

    I have so far only used it for 2 main purposes.

    1) Polaris altitude correction . You are basically lining up polaris through the center and estimate LHA of Cassiopeia trailing star. This is lined up with the "Y" axis graduated in + or Minui 40'. So the angle of LHAmeasured to the nearest degree or so ( a bit better with Vernia)  immediatedly gives the poalris correction to the nearest minute! 

    2) can be used to estimate longitude by measuring LHA kochab as per Tony Crowley book.

    Best wishes


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