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    Re: New compact backup CELNAV system
    From: Brad Morris
    Date: 2009 Feb 25, 16:53 -0500

    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



    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.


    --- On Wed, 2/25/09, nsg21@hotmail.com <nsg21@hotmail.com> wrote:

    From: nsg21@hotmail.com <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
    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
    > GPS and finding a simple way to do this. I think I have found a method
    > is simple, self contained, takes up little space, needs no almanac or
    > reduction tables



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