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    Re: transit vernier "least count"!
    From: Paul Hirose
    Date: 2005 Jun 5, 20:28 -0700

    Mike Burkes wrote:
    > Hi folks need your help! I realize photo is not very clear but I
    > determine the " least count" of the vertical circle reading is 6 sec of arc.
    > Is "least count" the correct term for the smallest reading?
    > http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=55807&item=7520967460&rd=1
    
    I think a 6 second vernier on the vertical circle would be way out of
    line for an instrument of this type. To me it looks like a 1 minute
    vernier in the photo. It's a bit blurry, but there are clearly 10
    graduations between "20" and "30" on the left half of the vernier.
    
    Note that even the classic Parkhurst theodolite, used by the U.S. Coast
    & Geodetic Survey for first-order triangulation, only had a 10-second
    vernier on the vertical circle. (The horizontal circle was read by a
    pair of microscopes with filiar micrometers, estimated to to .1 second.)
    
    One of my surveying textbooks says a 1-minute vertical circle vernier is
    usual on traditional American transits like that Gurley on eBay. The
    horizontal circle may be divided finer. Also, that book agrees with your
    usage of "least count" regarding the vernier graduations.
    
    I don't watch Gurleys on eBay that closely, but by my recollection the $200
    start price is pretty attractive. Granted, you'll never see the smart
    bidders until after the auction closes (they'll "snipe" the item), but
    *no* bidders after several days? I wonder if something is not kosher
    about this transit.
    
    
    

       
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