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    Re: Q: how to calculate refraction at higher altitudes on
    From: Chuck Taylor
    Date: 2002 Feb 28, 12:18 US/PACIFIC

    > I am specifically trying to determine the elevation of my house.
    >
    > I have a high quality Chelsea barometer, ...
    >
    > Given these constraits and tools, can I get a better estimate of
    > my elevation?
    
    Dan,
    
    I would recommend using your barometer instead of your sextant.  Obtain the sea
    level reading either from radio/TV/internet or by driving down to the water,
    then compute the altitude from that.
    
    I did a bit of research, and came up with a site that talks about constructing
    an electronic barometer:
    
            http://davidbray.org/onewire/barometer.html
    
    For calibrating the barometer, he gives the following formula:
    
      absPress = exp((log(1 - 6.87324e-6 * altitude) * 5.256)) * seaLevPress
    
    where "absPress" is the pressure at your elevation.  Here "log" means "natural
    log".  Solving for altitude, I came up with
    
     altitude = 145491.8*(1 - exp(log(absPress/seaLevPress)/5.256))
    
    That is for pressure in inches and altitude in feet.  It should be a piece of
    cake to program that on one of your HP calculators.  A linear approximation
    would be about 0.001065 inches of pressure per foot of altitude.
    
    There is a link on that page to a table which gives values for every 50 feet of
    altitude.
    
    Chuck Taylor
    Everett, WA, USA
    
    
    

       
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