NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant precision
From: Jared Sherman
Date: 2004 Sep 30, 20:30 -0400
From: Jared Sherman
Date: 2004 Sep 30, 20:30 -0400
<a) The
Russian manual recommends to rotate the drum
only in one direction, >
only in one direction, >
Alexandre, this is probably a writer's error in the
manual. With any "screw" movement like that of the drum, there is some slop in
the fit of the parts. So, if you are moving the screw "forward" on the arc, and
pass a certain point, it will physically read a certain number. But if you move
"backward" past that same exact point, and stop in exactly the same place--the
number will read differently. The drum (screw) will line up very slightly to a
different place, because now it is pressing up on the back side of the gear
teeth and helix, instead of on the matching cuts in the front side of
them.
So feel free to move the drum in both directions,
but once you make a reading going "this way", if you go past it go back and then
come forward again--so that all of your readings are either made while going
forward, or going backward. It doesn't matter which way you go--only that it be
consistent. And of course, that should be the same direction that you go in when
zeroing for index error as well.
If there is no slop at all in the machining, in
theory there will be no difference in which way you go. Or, the difference may
be so slight as to pay no mind. But if you are pressing for accuracy--always go
in the same direction.
