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    Re: Traditional navigation by slide rule
    From: Hewitt Schlereth
    Date: 2016 Jan 21, 13:23 -0800

    FWIW, I only used my adapted rule for the basic sin/cos formulas for Hc and Z. It definitely saves steps. I believe Greg agrees.

    I also pretty sure Gary has written on using the Bygrave formulas, which require tangents.


    On Jan 21, 2016, at 12:12 PM, Bob Goethe <NoReply_Goethe@fer3.com> wrote:

    My current thoughts on the Mark 1 Navigator's Slide Rule.

    SCALES:  dd.d vs. dd mm

    I think it was John Lasseter, the director of “Toy Story”, who said, “Digital projects are never finished; merely abandoned.”

    Keeping that back-door in mind, I am persuaded that the Mark 1 version of the Navigator’s Slide Rule should Have its trig scales divided by degrees and minutes rather than decimal degrees.

    SCALES:  Hewitt's Idea

    I am going to at least make a cardboard slide rule – and perhaps purchase both a K&E 4070-3 and a 4090-3 – to experiment with Hewitt's idea of having trig scales on both the body and slide of a rule, to see if it indeed speeds up calculations when doing Bygrave equations.


    When I am shaving in the morning, I ponder how K&E managed to get that terrific red line on their cursor.  I wonder if it might not be a strand of silk thread.
    But when I think of ways that building a cursor might be doable by a casual hobbyist like me, a couple of things come to mind.  First, I have no convenient way to produce or work with transparent plastic.  Second, I have already discovered that automotive glass shops are not really set up to work with tiny/thin pieces of glass.

    CURSOR:  Etching

    I see that Globe Scientific has managed to etch their name onto their slides.

    It is on my to-do list to contact them and see if they have the wherewithal to etch a single line down the middle of the slide.

    Failing that, I could try and etch the glass myself using a steel ruler.  However, I would feel better about the precision if I could get some company to do it with a machine than if I did it myself with some sort of tool I picked up at Home Depot.

    CURSOR:  Laser Printing on Transparency

    Another possibility is that I laser print a hairline onto a transparency, and then mount that on a piece of glass (such as a microscope slide). 

    If I did this, it might be good to mount the plastic transparency between two glass microscope slides.  It wouldn't do if somebody left the slide rule on a table in the sunshine, and the plastic deformed a bit, or even migrated its position.  Mounting between two slides might serve to keep it in place, and minimize deformations of the plastic.

    CURSOR:  Width of Slide Rule Cursor

    Time spent with YouTube on glass cutting suggests that, because of its thinness, I might regularly break a 75 mm microscope slide if I tried to reduce its length.

    Does anybody know of any sources of custom length glass that could be incorporated into a cursor?

    If not, rather than designing a rule and fitting a cursor to it, I may need to design the cursor first and then fit a rule beneath it.


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