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    Re: Measuring (and Calculating) Dip
    From: Bruce J. Pennino
    Date: 2013 Mar 11, 16:39 -0400
    For the American transit, I had vaguely remembered that in the "ole days" there were procedures to flip the scope, turn angles right, turn angles left etc.  I never did any of these things because I've never done highly precision work as required for a land survey, long distance surveys, or legal documents. I'm a civil engineer that does very simple / ordinary construction layout, mostly as a volunteer for Rail Trail work. Once I bought an EDM/theodolite the precision and accuracy was so much greater that specialized procedures became totally unnecessary for me. 
    However, for measurement of small vertical  angles,  technique becomes very important. My plan is now to set up the theodolite, make a set of readings "wire" coming down; another set wire going up.  Flip "gun" 180*, rotate 180* and redo.  I honestly don't remember  how my internal optical  angle scale functions in the "reversed" mode ie, whether the sign of the  angles will be greater or less than the previous mean value.  Maybe doubled?  I'll go read the manual and a good surveying book. Your comments are appreciated and I think saved me some work while increasing precision and total accuracy.
    ----- Original Message -----
    Sent: Monday, March 11, 2013 11:17 AM
    Subject: [NavList] Re: Measuring (and Calculating) Dip

    I wrote:
    > If you change faces, the effect
    > of index error has the same magnitude but opposite sign. Thus, the
    > difference of the face left and face right readings is the index error,
    > and the mean is free of index error.
    Correction: the difference between face left and face right is TWICE the
    index error.
    I filter out messages with attachments or HTML.

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