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    Re: US Navy and celestial...
    From: Stan K
    Date: 2017 Sep 15, 15:47 -0400
    An interesting spec on the Navy Mark II was that it has the largest usable arc of any sextant I know of.  The arc is graduated to 145 degrees, and the index arm can actually reach this point.  Sure, there wasn't much index mirror left to see at this angle, but it was there.  The Mark III, on the other hand, was graduated to a more typical 125 degrees, which it could reach.  Admittedly the extra range of the Mark II was only an advantage for artificial horizon sights, back sights, lunars (and that would be pushing it), and horizontal angles, all of which I suspect were not often (perhaps never) done by the Navy, especially since the time of the introduction of the Mark III.


    -----Original Message-----
    From: Paul Hirose <NoReply_Hirose@fer3.com>
    To: slk1000 <slk1000@aol.com>
    Sent: Fri, 15 Sep 2017 14:50
    Subject: [NavList] Re: US Navy and celestial...

    Back in the 1990s, when I was still on active duty (USAF, not USN), I
    looked up mil spec for the Navy Mark III sextant. The spec appeared to
    be a clone of a C. Plath. There was a name (maybe a trademark?) for the
    metal of their frame, and the mil spec required that same metal. I think
    it also called for their ergonomic handle.
    To me it looked like a case of "specmanship." Such manipulation of the
    military procurement system was an occasional tactic. You couldn't say
    "I want this model from that manufacturer." The correct procedure was to
    state the what properties the device had to possess. Then the supply
    people would search for the product that met your requirements at lowest
    cost. By carefully crafting the parameters of your request, you could
    guarantee the only match would be device you wanted.
    The mil spec for the Mark III included the test procedure. The sextant
    was clamped to a precision rotary table, with the index mirror at the
    center. A collimator, also attached to the table, was aimed into the
    horizon glass to simulate the horizon. A fixed collimator aimed at the
    index mirror simulated a star. By rotating the table you could control
    the altitude of the "star." Tests were made with and without shades. I
    forget the maximum permissible error.
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