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    Re: sextant index error measurement
    From: Frank Reed CT
    Date: 2006 Nov 9, 03:57 EST
    "I checked with a friend who worked in Arizona.  He said he had a
    "clear mental image of a range pole at a half mile looking like
    a snake through the transit", and that the more important angles
    were shot in the morning.  But . . . they kept working.
    Probably depends on the accuracy you need."
     
    Sure. As I've said previously, the 'normal' terrestrial refraction ranges from 0.1 to 0.5 (or so) minutes of arc per nautical mile. That's why you can only trust the dip of the horizon to about that level of accuracy. But for a few hundred feet, as in the laser test we've been discussing, the terrestrial refraction is about ten times smaller. And that's just the absolute refraction. For two beams side-by-side, the differential refraction is smaller again, by an order of magnitude. In short, it doesn't matter ...under these specific circumstances.
     
    -FER
    42.0N 87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars

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