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    SNO-T tests
    From: Alexandre Eremenko
    Date: 2005 Nov 21, 13:30 -0500

    Dear list members,
    I want to share some test results of my SNO-T.
    (It was bought in Fall 2004 "new", but made in 1990,
    has a factory certificate showing correction +10"
    everywhere on the arc, which is nonsense, of course.
    In summer 2005 I had it checked and certified by BOTH
    Freiberger and Cassens-Plath. Freiberger issued a
    certificate which shows the following corrections:
    
    10d 20d 30d 40d 50d 60d 70d 80d 90d 100d 110d 120d
    -4" -4" 10"  6" -1"  4"  5" -5"  4"  4"   3"   14"
    
    Cassens-Plath wrote only their usual
    "This instrument is free of errors for practical use".
    
    However my multiple careful observations (most of them under
    perfect conditions, from a balcony) indicate that there is
    some arc error as well as a visible backlash.
    (Of course this can always be attributed to insufficient proficiency
    of the observer, but consistency of the results I obtain seem to
    indicate that my proficiancy is not that bad).
    
    In all examples below the inverting 7 x 40 scope was used,
    I find it by far superior to the 3.5 x 50 Galileo scope.
    Sigma stands for mean quadratic error in a series,
    SD for the visible radius of the Sun.
    To avoid  unconscious bias in selection
    I include ALL results of the last week of which I have
    accurate records.
    
    IC from Sun, Nov. 17, average of 5 each:
    clockwise: -0.42' (4SD=64.72) anticlockwise -0.16' (4SD=64.78)
    sigma=0.16' in each case, true 4SD=64.8
    
    IC from Sun, Nov. 19, average of 5 each:
    clockwise or anticlockwise the same -0.4' (4SD=64.86', true 4SD=64.8')
    sigma=0.15', true 4SD=64.8
    
    IC from Sun, Nov. 20, average of 5 each:
    clockwise: -0.5', anticlockwise -0.4' (4SD=65' in each case, true 4SD=64.8')
    sigma=0.1'
    
    Index from a star (Rasalhague) Nov. 20.
    clockwise: -0.6', anticlockwise -0.2'.
    
    (This is typical for my index observations from stars.
    Sometimes I get -0.7 clockwise and -0.1 anticlockwise,
    but the average was always
    -0.4 or -0.5 during the last two weeks. In most cases I apply
    the average IC=-0.4 or so.)
    
    Deneb-Rasalhague distance, Nov. 20, 00:40 GMT
    Average of 4 clockwise 51d12.0' (sigma=0.0') corrected for index: 51d11.4'
    Average of 4 anticlockwise 51d11.6' (sigma=.2') corrected for index: 51d11.4'
    True distance: 51d11.4'
    
    Deneb-Rasalhague again, Nov 20, 01:00 GMT
    Average of either 4 clockwise or 4 anticlockwise: 51d11.0'
    Applying the average IC=-0.4' gives 51d10.6'
    True distance: 51d10.7'
    
    Deneb-Altair distance, Nov 20, 01:30 GMT
    Average of 4 clockwise: 38d00.9' (sigma=0)
    Average of 5 anticlockwise: 38d00.4' (sigma=0.2)
    Total average of all 38d00.6'. Corrected for IC=-0.4 gives 38d00.2'
    True distance: 37d59.8'
    So we have 0.4' overshot.
    
    Deneb-Altair distance, Nov 17, 01:25 GMT
    Average of 6 clockwise: 38d00.8 (sigma=0)
    Average of 6 anticlockwise 38d00.3 (sigma=0.3)
    Total average 38d00.6' Correction for IC=-.044 gives 38d00.2'
    True distance 37d59.8'
    So we have overshot 0.4'
    
    What can this be is not an arc error?
    
    Deneb-Vega distance, Nov 20, 02:40 GMT
    Average of 4 clockwise: 23d50.1 (sigma=0)
    Average of 4 anticlockwise: 23d49.9 (sigma=0.1)
    Total average: 23d50.0' correction for IC=-0.4 gives 23d49.6'
    True distance 23d49.5'
    
    Deneb-Vega dist., Nov 13, 23:40 GMT
    Average of 4 clockwise: 23d51.3, with IC=-.8 gives 23d50.5'
    Average of 4 anti-c:    23d51.0, with IC=-.4 gives 23d50.6'
    True distance: 23d50.4'
    
    Sun-Moon distance of 126 degrees, Nov. 20, 14:40 GMT corrected for IC=-0.44
    Errors according to Frank's calculator: 0.3', -0.1, 0, 0.1, 0.1.
    
    Sun-Moon distance of 137 degrees (maximum SNO arc allows! one can go
    a bit further, to 141 degrees by detaching the magnifying glass:-)
    
    Nov. 19, 14:40 GMT, corrected for IC=-0.4
    Errors according to Frank's calculator: -0.2', 0.1', 0.3'.
    (One blunder discarded, error 0.7')
    
    Mars-Moon distance of 40 degrees
    Nov. 18, 3:30 GMT, corrected for IC=-0.4'
    Errors according to Frank's calculator: -0.3', 0.8', 0.2', 0.7', 0.7',
    0.6' then checked the Frank calculator, and repeated the series, trying
    to see whether I can match somehow the numbers calculator gives:-)
     -0.1', 0.5', -0.1', -0.2', -0.5',
    0.3', 0.1', -0.1':-)
    
    Mars-Moon distance at 16 degrees
    Nov 13, 1:30 GMT, IC=-0.4'
    Errors: 1.0', 0.6', 0.8', 0.2', 0.7'
    
    Same, with Bill's Astra, same evening, with the SAME inverting scope:
    Mars-Moon at 16 degrees, Nov 13, 1:30 GMT IC=+0.35
    Errors: -0.1', 0.1', -0.1', 0.2', -0.1'
    
    Can I conclude that my arc has a huge bump at 16 degrees?
    
    However:
    Venus-Moon November 7, GMT 0:30 at 15 degrees, IC=-0.4
    Errors: -0.1', 0', 0'.
    
    Mars-Moon distance Nov. 18 at GMT 3:20, at 40 degrees, IC=-0.4 (SNO again)
    Errors: -0.1', 0.5', -0.1', -0.2', -0.5', 0.3', 0.1', -0.1'.
    
    Sun, art horizon, oil over syrup, Nov. 20, 19:20 GMT IC=-0.4, watch exact.
    Antickockwise, UL:
    
    19:28:20  48d42.8'
    19:29:50  48d25.3'
    19:31:00  48d10.9'
    19:32:32  47d52.9'
    19:33.54  47d36.7'
    
    Averages: 19:31:07 48d09.7'
    Error: -0.2 (undershot). But actually this means -0.4 because
    the measured altitude was divided by 2.
    
    Any comments?
    (I can supply more details on each observation if anyone is interested
    I would be very interested to see analogous data posted (or sent to me)
    by other people practicing without real horizon).
    
    Disclaimer for George:
    I understand that the issues discussed here are far from the
    practical needs of a small-boat navigator:-) Still I think these are
    proper questions for discussion on this list. My concern is whether
    I can take reliable Lunars under good conditions from land to 0.2' precision,
    and whether it is possible at all, and whether it is possible with
    my SNO-T.
    
    Alex.
    
    
    

       
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