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    Re: Using a slide rule for celnav
    From: Gary LaPook
    Date: 2014 Jan 20, 01:03 -0800
    If you are using the normal cosine formula to compute Hc then you have to write down an intermediate value since you have to add the two values together.

    But to answer your question. To multiply two sines together,
    1,center the slide.
    2, move the cursor to the first value on the sine scale.
    3, move the slide so that the "1" is lined up with the cursor.
    4, move the cursor to the second sine value.
    5, read out the result on the "D" scale in line with the cursor.

    The same thing works for cosines.

    gl



    From: David Cortes <dcortes{at}rwlw.com>
    To: garylapook---.net
    Sent: Sunday, January 19, 2014 10:48 PM
    Subject: [NavList] Using a slide rule for celnav


    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, etc.?
    
    David
    
    -----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{at}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. :)
    
    -FER
    
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