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    Re: New compact backup CELNAV system RENAMED Accuracy of Bygrave Slide Rule
    From: Frank Reed
    Date: 2009 Apr 14, 22:10 -0700

    Brad, you wrote:
    "There is a bit of a conundrum here.  The amount of work needed to extract a 
    value from a set of tables varies little, except if you are using Sumner Line 
    of Position or earlier.  There will be some quibbling about the arrangement 
    of the tables being "inconvenient" in HO229 or that there is no interpolation 
    required of HO249, but at the end of the day, you have spent just a few 
    minutes in the tables themselves.  Why not get the maximum resolution that 
    you can?"
    If I understand you correctly (and please correct me if I haven't), you're 
    asking why someone would prefer one of these compact slide rule-style methods 
    of reducing sights considering that they have slightly reduced accuracy in 
    some cases when the amount of work is the same. So why not just bring along 
    HO229 then? There are a number of answers to this that I can think of. Here's 
    a couple...
    First of all, this isn't just a theoretical game (not to state the obvious!). 
    If someone has an intention to do celestial today, very practical 
    considerations come into play. Real navigation is done by GPS, and for that 
    you should cut no corners: carry spare hand-held GPS receivers, bring lots of 
    batteries, etc. Since you don't really "need" celestial, when the time comes 
    to consider what to pack on your "three hour tour" or "three week adventure" 
    the bulk of those big tables could be a serious deterrent. Do we bring the 
    cooler full of sandwiches or do we bring HO229? So "these days" I think there 
    are real benefits in going light (in terms of weight) and Gary's rather cool 
    method is certainly light. The modest reduction in accuracy that may result 
    is probably not important considering how far it is from the accuracy of GPS 
    Second, since celestial is very much a secondary, even tertiary, method of 
    navigation in this day and age, the choices people make for using certain 
    types of sight reduction is much more a matter of personal interest than 
    absolute accuracy. I suspect that a lot of navigation enthusiasts who cut 
    their teeth on HO229 would find great pleasure in using one of these slide 
    rule-like methods. If for no other reason, then because it makes something 
    old and routine, new and interesting again.
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