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    Re: Red knob on micrometer
    From: Luc Van den Borre
    Date: 2014 Jun 23, 10:59 +0200

    On 23/06/2014 4:56, Frank Reed wrote:
    > A few months ago, someone asked me what the "red knob" on the micrometer
    > on his sextant was for (see the image below). I have finally remembered
    > to post this. Is it used to adjust out index error or something like
    > that? That was my quick guess.
    Yes, the red knob locks the micrometer drum in place on the shaft of the
    tangent screw. To release the micrometer drum, hold it tightly while
    unscrewing the red knob.
    Cassens & Plath advertise this as a convenient way of correcting both
    index error and dip combined. I don't have dip (artificial horizon), but
    I do like it, because it allows me to get rid of the tiny bit of index
    error that is left after adjusting the mirror as well as I can.

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