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    Re: Finding IC for A-12 bubble sextants
    From: David Pike
    Date: 2021 Oct 12, 12:26 -0700

    That’s a great mounting for an A12 Ed Popko.  I’ve been figuring upon making myself something like that for a while, but I wasn’t sure of the A12 thread.  Guessing that it might be ¼”UNC, I’d just ordered two ¼”x2.5”A2 machine screws from eBay to check when I remembered that as a Kid in the 50s I’d been sufficiently keen on photography that I’d also bought a camera tripod.  It was German in those days, not Chinese.  Maybe that might have a ¼”UNC thread.  After a 15-minute search, I gave up, but 15 minutes after that, I found it while I was searching for something else.  Sure-enough the ball-head fitted the A12, so I thought I might as well see if the arrangement would work to centre the sextant bubble.  It did, except I had to move the tripod legs as part of the levelling, so it might not work outdoors.  Handy tips I found for basic levelling before fine levelling through the eyepiece were.  The bubble will be close to central vertically when the top of the grip handle is horizontal.  The bubble will be very close to central laterally when a spirt-level laid across the two upper sides of the A12 is also level.  Sorry about the quality of the bubble photograph but aiming a hand-held smart phone down the eyepiece of an A12 is even harder than levelling a hand-held A12.  One for the experts, “Does my bubble look big in this?”.  DaveP

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