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    Re: Measuring (and Calculating) Dip
    From: Bill Morris
    Date: 2013 Mar 8, 20:07 -0800

    Hi Bruce and Brad

    When I checked it, the theodolite turned out to have a substantial index error, quite enough to account for most of the differences between the dip from the NA and the dip I measured. Please discard the results. I suspect the rough gravel roads over which I have to travel may have upset something, so the instrument will travel comfortably seated rather than on the floor in future.

    I have negotiated another visit to the beach with the staff (wo)man and have removed nearly all the index error, a none-too-easy task with a bubble that has a sensitivity of 15 seconds per 2.5 mm movement. I will take readings off each face (not strictly necessary with the T2) if my assistant's patience will allow it.

    While the Wild T2 theodolite reads to single seconds and claims an accuracy of 0.4 seconds for the circles I very much doubt that a single vertical reading can be relied on to better than 5 to 10 seconds, not least because the horizon seen through a high quality x28 telescope is not a straight line but a scintillating line of wave tops and also because taking a reading depends on vernier acuity which also has its limits and variations.

    Bill Morris
    New Zealand
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