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    Re: Compass Error Corection
    From: George Huxtable
    Date: 2010 Jul 2, 14:16 +0100

    If you want to trace back into this series of postings, it helps to be 
    aware that some have been spelled "Compass Error Corection", as is this 
    one, and others, correctly, as "Correction". If you search under either 
    threadname, you will find only some. Searching under "compass error" should 
    find all.
    
    ====================
    
    This is a response to a strange posting by Joe Schultz, on 1 July. It 
    included the following statements-
    
    "...given up on this list (as do most practical navigators) ..."
    
    "...you're in the wrong place for combining innovation and practical 
    navigation.  This list has been taken over by (mostly) dreamers and 
    historians, and you went right over their heads.", dismissing those 
    "dreamers" at several points in his text.
    
    In which case, I wonder why Joe Schultz continues to grace our list with 
    his presence, and his postings. How does he manage to overcome his 
    distaste?
    
    =======================
    
    As (I hope) one of that select category of "dreamers and historians", 
    perhaps I have a bit of explaining to do, to Joe Schultz.
    
    The US Navy may well have a particular problem, in that every move a man 
    makes is prescribed by regulation. Even when those regulations make little 
    sense, as Byron implies is the case, it may well be a Herculean task to get 
    committees to admit it and make changes.
    
    The rest of the seafaring world is less hidebound. I can't speak for the 
    merchantmen, who know doubt have their own, less rigorous, rule books. But 
    the recreational sailors ("yachties", in Joe's words) are free spirits, in 
    this respect. They have the privilege of being able to apply common-sense 
    to their navigation, and by and large, that is what they do.
    
    So, for example, this one-in-sixty approximation, for a sine or tangent of 
    a small angle, about which much has been made by Byron and by Joe, is 
    familar stuff to British small-craft users, even those who don't admit to 
    knowledge of trig but still apply it to narrow triangles in chart plots. 
    It's taught in all such evening classes, here in the UK, with the important 
    proviso that it applies, approximately,  to angles of only a few degrees, 
    depending on the accuracy being called for. On this side of the Atlantic, 
    the matter would be regarded as trivial: just as Apache Runner has implied 
    in a recent email.
    
    And so, the linked file, provided by Joe at 
    http://www.fer3.com/arc/imgx/1-in-60.gif, adds little information. Indeed, 
    I've puzzled over that page for some time before taking in its message, 
    because there's no explanation of what it is trying to do.
    
    He writes the equation sin A = U / D, which would be valid enough for a 
    right-angled triangle, but then attempts to illustrate it with a triangle 
    which is deliberately drawn to be very far from right angled, and to which 
    that expression would certainly not apply. A fine recipe for sowing 
    confusion in the mind of a reader.
    
    What's listed as "step 1" is not in fact a step in the calculation of error 
    at all, but establishing a rule for minimum distance of a charted object to 
    meet certain requirements, which happen to be met in one of his following 
    examples, not in the other.
    
    And that criterion differs, considerably, from what Byron considered to be 
    that minimum distance, in his posting of 13 April, when he wrote-
    
    "All that is required is to estimate your position alongside the pier, 
    determine how accurate your position is known + or - 10, 15, 20 yds etc. 
    Once this value is known double it and multiply by 60 ‘ result is the 
    minimum distance you want an object to be in which to obtain a bearing to".
    
    Byron didn't state, there, what bearing accuracy this test was expected to 
    provide, but further down that page it turns out to be a quarter of a 
    degree. Indeed, if a quarter-degree was intended, shouldn't Byron's "double 
    it" really be "quadruple it"? However, this  depends on whether the 
    position inaccuracy is defined as how far from the presumed position the 
    observer may be, or alternatively twice as far; the overall range of 
    possible positions, between one direction and its converse. Byron doesn't 
    say, and Joe hasn't clarified that ambiguity.
    
    =========================
    
    Joe Schultz then presumed to offer Byron advice, including - "Be careful 
    with the numbers you use in your examples, so you don't inadvertently 
    confuse the reader" Which is a bit rich, considering his own linked file.
    
    And continued- "Write for your audience.  The combined underway fix and 
    compass error can't be done by merchies/yachties, for example, unless an 
    athwartship range is shot while steering another range".
    
    He would do well to follow his own advice. Who make up this audience? One 
    is me, a native speaker of English, of a sort, though a rather different 
    sort to that of Joe and Byron. Others on this list are not native-speakers 
    of English at all, but manage well enough to put many of us to shame. But 
    I, for one, have to guess at Joe's meaning when he writes- "...an 
    athwartship range is shot while steering another range." Does a "range" 
    mean the same as an azimuth, I wonder, or a direction, or a course, or what 
    I would know a "transit"? Where I was brought up, a range is some sort of 
    measure of distance, not direction. And what on Earth are "ring knockers 
    and trade schoolers"?
    
    Two contributors to this list, who give me most difficulty in interpreting 
    what they write, are Byron Franklin and Joe Schultz. Both, it so happens, 
    are US Navy trained. Is there something special about US Navy language, 
    larded as it is with acronyms, jargon, and homely folkiness, which makes it 
    hard to follow? Do others have the same difficulties that I do?
    
    George
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    
    
    
    

       
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