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    Re: New compact backup CELNAV system
    From: Ark Shvetsky
    Date: 2009 Feb 26, 12:04 -0800

    Gary, you are very right about slide rulers. I attended the school and college 
    and got my degree in old country using slide ruler for most complicated 
    calculations, including Runge-Khutta methods, Euler's and McLoran's sets, 
    thermohydraulic and strength of material, applied gasodynamics calculations.  
    Always to the two digits after the "comma" (it wasn't point, as in the USA).  
    And of course, almost everything was built to use slide ruler as the major 
    calculation tool-never failed.   Old wise Lecky in his famous "Wrinkles..." 
    mentioned unnecessary desire of young navy officers to do calculation with 
    extra accuracy which is just not needed, unless it is done for fun.,  
    ----- Original Message ----
    From: Gary LaPook 
    To: NavList@fer3.com
    Sent: Wednesday, February 25, 2009 10:54:28 PM
    Subject: [NavList 7436] Re: New compact backup CELNAV system
    Nothing in this world is perfect. You guys have identified a problem 
    that does not arise in practice with this model of the Bygrave. To the 
    level of accuracy expected from this device, the scale distortion 
    produced errors that you guys are concerned about just don't occur. The 
    errors you are concerned about "fall into the noise" of the two minute 
    expected accuracy. I have made 12 of these and worked more than a 
    hundred sample problems and checked the results against the results from 
    a digital calculator and all the results agreed within two minutes of 
    arc. Two minute accuracy is sufficient for practical off shore 
    navigation and is certainly good enough for a "backup" system. Even my 
    ten inch long Keuffel & Esser 4080-3 slide rule can produce calculated 
    altitudes that are accurate enough for off shore navigation but not at 
    all places on the scales as they become bunched near the ends. What 
    makes this flat version of the Bygrave very good for celestial 
    navigation is that the cotangent scale is not ten inches long it is 
    351.5 inches long, 29.3 feet, 8.9 meters! Having logarithmic scales this 
    long allows for much greater accuracy than from a ten inch long slide 
    rule and they consistently produce results agreeing within two minutes 
    and often are in exact agreement.
    Many of the buildings you stand in, many of the airplanes that you fly 
    in and most of the bridges that you drive across today were designed 
    with the use of slide rules so they have for many years provided 
    calculations that we still rely upon for our daily safety.
    So make one and give it a try, just don't expect agreement within 
    one-tenth of a minute and you will see the usefulness of this for a 
    backup celnav system. As it says on the side of the medicine bottle, 
    "safe when used as directed."
    Brad Morris wrote:
    > This problem does not exist on a “real” Bygrave because the cylinders 
    > are stiff and remain concentric with each other. I do recognize the 
    > difficulty in getting the scales mounted and keeping them referenced 
    > to each other when going through the zig-zag pattern of solution.
    > I think that local distortions of the one scale to the other will 
    > clearly result in errors. Slide rules in general work when the one 
    > logarithmic scale is referenced to another logarithmic scale. 
    > Distorting one or the other cannot be permitted. NSG21 is absolutely 
    > correct.
    > I remember being the last class to take slide rule instruction in High 
    > School. When you use a slide rule today, most people think of it as 
    > black magic and have no idea how it works. Further, the electronic 
    > calculator leads young engineers to give me as many decimal places as 
    > their calculator does, without judgment as to the meaning of those 
    > digits. Empty resolution without addition to accuracy.
    > Best Regards
    > Brad
    > *From:* NavList@fer3.com [mailto:NavList@fer3.com] *On 
    > Behalf Of *Gary LaPook
    > *Sent:* Wednesday, February 25, 2009 4:39 PM
    > *To:* NavList@fer3.com
    > *Subject:* [NavList 7430] Re: New compact backup CELNAV system
    > I haven't seen the problem you mentioned. I sealed the Cotangent scale 
    > in normal plastic protection sheets (about one buck each at Fryes) 
    > used for protecting documents which are quite rigid. I will experiment 
    > with bending the scale and working a sample problem and get back to you.
    > gl
    > --- On *Wed, 2/25/09, nsg21@hotmail.com //* wrote:
    > From: nsg21@hotmail.com 
    > Subject: [NavList 7427] Re: New compact backup CELNAV system
    > To: NavList@fer3.com
    > Date: Wednesday, February 25, 2009, 9:47 AM
    > I would like to share some experience in using this (transparency over printed)
    > style of the slide rule. The surface it is placed for calculation MUST
    >  BE
    > ABSOLUTELY flat. Even small warping of the surface (such as normally found on
    > small plastic tables) leads to big errors in calculations.
    > From: glapook---NET
    > Date: Tues, Feb 24 2009 12:06 pm
    > > There are often posts on the Navlist regarding using celestial as a backup
    > to
    > > GPS and finding a simple way to do this. I think I have found a method
    > that
    > > is simple, self contained, takes up little space, needs no almanac or
    > sight
    > > reduction tables 
    > ...
    > >
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