Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Sextant precision
    From: Jared Sherman
    Date: 2004 Sep 30, 20:30 -0400
    <a) The Russian manual recommends to rotate the drum
    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.
       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site