Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    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')
    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?
    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.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site