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    Re: Northern Limits of Magnetic Compass Usefulness
    From: Frank Reed
    Date: 2019 Feb 7, 13:09 -0800

    I wrote previously:

    There's another way to draw all the curves for a sundial. Get yourself a little light bulb on a stick (I have used handheld Halloween toys for this), some thin tape, and a wide, short clear plastic cylinder (like the ones that 25-50 CDs are shipped in). With those tools and some simple computation, you can produce a nice analog computer which can project the lines required for a sundial onto any surface facing in any direction.

    Here's a sketch to illustrate the idea. The Sundial layout projector can be used to project the lines, both hour lines and month lines, onto any surface. Trace them out. Then replace the projector with a stick to serve as the gnomon. And there you have it. A sundial, which can be used in reverse, as a Sun compass.

    Frank Reed


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