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    Re: Sextant Repairs
    From: Robert Eno
    Date: 2014 Jan 15, 09:19 -0500
    Excellent idea Frank. I don't know why it never occurred to me to try just that. I gave up on the brass cylinders and other objects long ago and have generally used the eyeball method for adjusting/confirming perpendicularity. I am going to try your suggestion for the fun of it. This makes perfect sense.

    ----- Original Message -----
    From: Frank Reed <FrankReed@HistoricalAtlas.com>
    Date: Wednesday, January 15, 2014 4:18 am
    Subject: [NavList] Re: Sextant Repairs
    To: enoid@northwestel.net

    Gary, you wrote:
    "Don't be afraid that you will hurt the instrument, they are designed to be adjusted by the navigator, that is the reason that wrench came with it."

    Yes. Excellent advice.

    By the way, for one and all, I recently found a really nice solution to the "equal-sized objects" problem for the index mirror perpendicularity test. I've previously recommended a pair of dice or a couple of stacks of nickels. And those do work well, but I've noticed that these choices are rather confusing especially for beginners. They're too similar. The cylinders you can buy for this purpose are even worse. The problem is that they look identical. When you see the direct and reflected image in the test, it's really quite tough to recognize that you're seeing two separate items. While talking about this with a class last Spring, I discovered two objects right in front of me that work much better. They were two whiteboard marker caps (a.k.a. "magic marker" caps). One was blue, the other green, and when they were placed at the appropriate spots on the arc, it was very easy to distinguish one from the other. And of course since they are the same size to high precision with a couple of cleanly-defined levels, they're ideal for the test. A couple of lego blocks or similar plastic toys in that size range would work just as well. The key difference that I am suggesting is that we pick two that are different colors. It really helps!


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