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    Re: Double vial horizon prototype
    From: Bill Morris
    Date: 2012 Jan 11, 17:28 -0800

    Geoffrey

    "For the avoidance of doubt" (no, I'm not a lawyer!)a ten second level nowadays means that for 10 seconds of tilt, the bubble moves through one 2.5 mm (formerly 1/10th inch)division. The plate level of my Wild T2 theodolite, which reads to single seconds, is of 20 seconds sensitivity and that for the vertical circle is effectively of 15 seconds sensitivity. With fine-pitch levelling screws from which any tendency to wobble has been removed, it is the work of a couple of minutes to level a mirror, provided one approaches the task systematically.

    Bill Morris
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