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    Re: Making an artificial horizon, and leveling thereof
    From: Alan S
    Date: 2011 Jan 26, 14:24 -0800

    George:

    If the weather around here ever breaks, clear sky, no snow, less cold than it has been, and I survive a really rotten cold I somehow acquired, I will go out and shoot some more with my AH, concentrating on a particular roof line visible from my apartment complex, though the relatively short distance to it, from my sighting position will have to be lived with. It's difficult to move a house, epecially one that is occupied.

    As to my proceedure, which possibly I faild to describe clearly, note the following.

    1. Micrometer is "zeroed"
    2. Same for index arm.
    3. Sighting on, locally, the afore mentioned roof line, turn the micrometer until an unbroken lin
    4. Read IE from micrometer. If reading is between zero and 10, as you mentioned the error is "on the arc", and I subtract the reading from Hs. If the reading is between zero and 50, say 56, I subtract 56 from 60, leaving 4, which is the IE, being "off the arc" I add to Hs. Height of eye is not considered. Sun shields are rotated out of line of view.I hope this clarifies the maddness of my method.

    As to inconstiencies in IE, there are several possibilities that come to mind. One is "old eyes" they being 78 years of age, and not as sharp a once they were. Another is the possibility of my misreading the roof line, perhaps making an IE correction where none is needed. I do not however think that having obtained a reading, that I'm misunderstanding or misconstruing it, taking what is actually "on the arc" for "off the arc".

    George, you had asked for a reading of actual sea horizon IE's. The following are some obtained last fall in October 2010, at Emerald Isle, North Carolina, coordinates 34D 39.4M North x 77D 03.6 M West. I can send more if needed.

    9 October around 0900 IE {at} start 1.0 On, IE at end of shooting 2.2 on
    9 October around 1400 " 2.0 On " 1.6 On
    6 October around 1500 " 0.6 On " 0.0
    6 October around 1100 " 0.6 On " 1.4 On
    5 October around 1500 " 1.6 On " 1.4 On
    5 October around 0900 " 0.4 On " 0.4 On

    for whatevrer it might be wrth, I had had some correspondence earlier on with a gentleman, who said he was familiar with Emerald Isle, and the general area, having done sextant shots from a couple of miles away from my location. He made mention of the "sea horizon" there not being as good as one might think this due to low handing clouds tending to obscure the sea horizon viewed from the beach, one would be looking generally south. The referenced clouds caused by The Gulf Stream. For all I kniow, he was entrirely right, but I suspect low hanging clouds or not, the sea horizon at the beach is better than what one might have to work with in and around Pittsburgh.
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