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    Using a slide rule for celnav
    From: David Cortes
    Date: 2014 Jan 20, 01:20 -0500

    To Navlist:
    I learned how to use a slide rule back in high school, and it's been 45-plus 
    years.  Can some of you old-timers tell whether it's possible to multiply sin 
    by sin or cos by cos, etc.  n one continuous operation, without putting the 
    rule down to write down the number of the first calculated sin or cosin, 
    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Frank Reed
    Sent: Monday, January 20, 2014 12:13 AM
    To: dcortes@rwlw.com
    Subject: [NavList] Re: What is a "Class A" sextant?
    Hi Brad,
    My understanding of the Kew "Class A" rating was that it was an overall 
    rating. It was the certification required for sextants given to Royal Navy 
    cadets. It combined several factors, and the instrument had to meet various 
    standards on several tests. 
    You may remember a NavList discussion a few years back about tables of "star 
    distances" published in about 1905 for use with Lord Ellenborough's method of 
    testing sextant arc error at sea (*). In the introduction, the authors say 
    that a "Class A" certification implies among "other things" that the 
    centering error (or "arc error" as we would call it today) amounted to less 
    than 1' of arc maximum. Classes B and C would presumably permit progressively 
    greater arc error, and this same source says that the sextant would be 
    "rejected" (in other words, worse than class C) if the arc error was greater 
    than 3'. 
    *that discussion was in March 2010, and here's my first message on thee 
    subject, specifically addressed to you personally, in fact. :)
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    Attached File: http://fer3.com/arc/imgx/class-A-sextant.jpg
    : http://fer3.com/arc/m2.aspx?i=126560

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