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    Re: What is this
    From: Frank Reed
    Date: 2008 Feb 29, 22:37 -0500

    The photos are rather low resolution, but I don't think those are mirrors on
    the back side. They look like "mounting points" of some sort (if so then the
    "frame" was relatively mobile while the "arm" would have been fixed in
    position). Perhaps this device was mounted on an artillery piece for
    measuring angle of elevation (?).
    
    You might consider asking the seller for a better photo of the scale, or if
    they're not skilled with the digital camera (which seems likely from the
    photo quality) maybe you could ask for a description of the markings on the
    scale. If it's a true reflecting instrument, like a navigator's sextant or
    octant, then the angles marked on the scale would be twice the angle
    measured at the center of rotation. If instead it's just a fancy protractor
    with a sighting tube, then the angle on the scale would be the same as the
    angle at the center. Second, is there a vernier scale on the metal plate
    attached to the arm? If not, then the device was probably only intended to
    measure angles to the nearest degree or so.
    
     -FER
    www.HistoricalAtlas.com
    
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