Hello,
To make it short.
If the bubble illumination assembly is not inserted in the sextant you can remove the bubble assembly by just twisting it a degree or two and pulling on it.
If the bubble illumination assembly is present, remove it first as the bulb interferes with bubble assembly when you pull it out.
If the bubble illumination assembly is stuck, then proceed as descried here;
To adjust the sextant, just back off the screw (with an Allen or similar wrench) that links the index mirror on this axis to free the mirror and reposition it to a correct postion for instance using polaris or during LAN. When the bubble is centered and the vernier indicate the precomputed reading, tighten the screw back.
You may then fine tune the index error by adjusting the vernier which is position with two screws at boths ends.
Good luck and please keep us posted on your progress.
JPP
--- On Wed, 9/22/10, John Brown <jdb0302@yahoo.co.uk> wrote:
From: John Brown <jdb0302@yahoo.co.uk>
Subject: [NavList] A-12 Bubble Sextant (Octant)
To: NavList@fer3.com
Date: Wednesday, September 22, 2010, 4:09 PM
I have recently bought a Link A-12 sextant on ebay - serial number 101. It appears to be in excellent condition, with no obvious damage to the gear train, index arm/mirror or vernier. The index arm moves freely throughout its range along the arc, with no binding or other signs of distress. The bubble assembly does not have the two knurled screws which are shown in the manual for retaining the assembly in the housing. Perhaps this was normal in the earlier production models. I have so far been unable to remove the bubble assembly, although I haven't made a really serious attempt to do so.
Unfortunately the instrument is in error by about 15 degrees.
I would appreciate any suggestions that might help me troubleshoot this problem.
Perhaps Dr Kolbe might respond? I bought the sextant after reading some of his posts and on-line papers about navigating in the Libyan desert.
I was a professional marine navigator and own C.Plath and Freiberger
marine sextants, now occasionally used at sea. I have also owned a Mark IX bubble sextant for many years for use in Saudi Arabia in pre-GPS days, inspired by DN Hall's 'Simple method of Navigating in Deserts' from The Geographical Journal in 1967.
Any help with my new purchase would be much appreciated! (I am in the UK).
Thanks - this is my first post on this excellent forum.
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