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    Re: Lunars: 10/27/2013
    From: Frank Reed
    Date: 2013 Oct 29, 10:09 -0700

    Sean you wrote:
    "Using a handheld GPS and double checking with Google Earth, I found the elevation of my yard to be 40 feet. "

    Ah, that explains it. Just to clarify, did you use the height from the GPS alone or from Google Earth given your latitude and longitude? If the height came from the GPS, bear in mind that this can be rather inaccurate. In any case, as I already noted, you don't need height of eye for clearing lunars unless you have measured the altitudes.

    "I am about 5 feet 10 inches tall."

    Nearest foot for height of eye is all you ever should expect.

    There is one little wrinkle in clearing lunars involving height above sea level. In my online clearing tool, there is a hint for this, but no more. Where you enter air pressure, it says "Pressure(SL)". This is a reminder that the pressure should be measured with a barometer adjusted at sea level. Reported air pressures are actually extrapolated to sea level so that pressures in variable topography can be compared. In other words, if one meteorological station is located on a small mountain, say, 2500 feet above sea level, and another is in a neighboring valley 1000 feet above sea level, the altitude component of the pressure difference is normally subtracted out when reports are made from the mountain location. If you live at high altitude, you can't use your local meteorlogical barometric pressure directly. You have to use the pressure that would be reported by a barometer that has been correctly adjusted at sea level and then transported to that altitude. Or equivalently, you have to subtract out the altitude correction applied in meteorology to high altitude barometers since the reported air pressure is not the true air pressure.


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