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    Re: What is a "Class A" sextant?
    From: Hewitt Schlereth
    Date: 2014 Jan 21, 12:15 -0800
    I note the last rating is for 105 degrees. Could the fact it could not read the full 120 degrees have made it be graded an octant?

    Hewitt

    On Jan 21, 2014, at 12:08 PM, "Brad Morris" <bradley.r.morris---.com> wrote:


    Hi Noell

    This is consistent with what we have learned so far.  I agree with Frank that its a *combination* of parameters

    One parameter is resolution.  It appears that it must resolve to better than or equal to 10".  10" was the statement found on the internet.  0.1 minutes is 6" so micrometer sextants will easily fulfill this requirement.  Yours at 15" does not.

    Another appears to be accuracy.  Frank thinks it to be 1'.  We have a random internet memory from a Commonwealth Navy stating 30".  Your zero-zero sextant passes this requirement.

    So of the two requirements, it fails one.  I expect this is like Frank says, it knocks you down a grade.

    There will be other conditions that we don't know about yet.  That is why I'm ever so hopeful that Dr. Dunn can help us with a complete list of requirements.

    Perhaps other board members have NPL (or Kew Observatory) certificates and would be willing to share.

    Brad

    On Jan 21, 2014 2:37 PM, "Noell Wilson" <noell_wilson{at}southwire.com> wrote:

    This is just another data point.
    Attached is the 1912 calibration sheet from Kew Observatory, preprinted "Class B", and stating 0'0" for all angles listed.
    So - 0'0" is not the criteria.
    This Weilbach vernier sextant has a minimum reading differential of 15" so maybe one vote for precise measurement capability - not necessarily accuracy.
    It's not an octant as the sheet says. The arc goes to 120 degrees but the arm stops a few degrees shy of full scale. It's an almost-sextant.
    Regards, Noell
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