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    Re: Fwd: Re: Sextant accuracy with short distance to horizon
    From: Dan Hogan
    Date: 2001 Jun 26, 3:13 PM

    On 26 Jun 2001, at 16:49, Michael Wescott wrote:
    
    > Dale Tilson wrote:
    [Snip Aussie bit]
    > >
    > > OK, guys, I'm new at this so somebody help me out.
    > >
    > > I thought the "dip" correction was necessary because the horizon isn't
    > > level with your height of eye.  Aren't we actually trying to measure
    > > altitude above a line horizontal with the line-of-sight?  If so, our Aussie
    > > friend would only need to find a perch so that his eye was level with the
    > > fenceline.
    >
    > He'd need the fence to be level and to take his sights with the eye at the
    > same height as the fence; in which case "dip" is 0. If either condition fails
    > then the dip will be different depending on where on the fence the sight is
    > brought down. That said, distance helps a lot. If the fence is 5 ft away, an
    > inch off in the height of eye makes an error of about 58 minutes. At 20 ft
    > it's 14' and at a half a mile it's 0.1'
    >
    > > If not, somebody straighten me out quick, because I was gonna set up an
    > > observation post in the back yard based on that premise.
    >
    > You'll probably get better results with an artificial horizon. Say a pan
    > of water or (my favorite) glycerin.
    
    As much as I can remember, He owned what is called a "Station", the fence was
    more than  amile from his proch AND it was level, he had that part built on
    purpose.
    >
    >
    > --
    >         Mike Wescott
    >         Wescott_Mike{at}EMC.COM
    
    
    
    Dan Hogan
    dhhogan{at}verionmail.com
    

       
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