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    Re: Altitude with artificial hirizon
    From: Greg Herdt
    Date: 2021 May 21, 11:18 -0600
    Good morning, Doug.  I am located near Albuquerque, NM at an altitude of roughly 5290 ft, somewhat extreme from a backyard navigation perspective.  Using the standard formulas, I have generated my own refraction correction table for this altitude and a range of temperatures.  Depending on the temperature and height of the body above the horizon, I need to correct the refraction from the Nautical Almanac by anywhere from 0.1 up to about 1.2 minutes.  I primarily do this for lunars and shots with my artificial horizon.  From what I have read, it appears that many of the 19th century lawmakers used temperature and pressure measurements to correct their shots.  Best regards, Greg

    On Fri, May 21, 2021, 9:46 AM Doug Faunt <NoReply_DougFaunt@fer3.com> wrote:
    I'm pretty sure the altitude of sights has been discussed, but I wasn't paying attention and can't find it.
    Apparently David Thompson used an artificial horizon, pretty obviously.
    How much difference would his altitude effect his sights?  
    Since I'm up here in the PNW on LADY WASHINGTON, the prototype of which traded on this coast in that period, we've been discussing all the exploration.
    Best, doug

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