NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant Calibration
From: John Rae
Date: 2006 May 15, 16:11 -0700
From: John Rae
Date: 2006 May 15, 16:11 -0700
Just to add my two-bits worth to the
discussion.
Some time ago I obtained a second-hand MAC Japanese
sextant. Like many sextants, this instrument has both a separate
adjustment knob and a micrometer drum on the same shaft.
On first using this sextant, I found that when the
drum micrometer wheel was set at zero, the index mark on the arm was about
half-way between the degree marks on the arc. This could easily cause a
misreading error. So by using the screwdriver adjustment on the
micrometer screw/drum knob, I was able to adjust the micrometer drum to read
zero when the arm markings were in alignment. Then it was a time consuming
but simple job to reset the mirrors so that the IC was acceptably
small.
The IC seems to stay at a stable reading, but I
check it each time I use the sextant, an almost automatic
task.
