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 calibration in the workshop
    From: Fred Hebard
    Date: 2008 Jan 13, 20:49 -0500

    I was busy with finishing procrastinated work when that very nice
    post came by, and didn't comment.  Thanks to Frank for resuscitating it.
    
    I'd just like to comment on one thing regarding these determinations
    of sextant error at fixed intervals along the arc.  One would expect
    that some smoothly varying curve passing through the points would
    describe the errors, so that one could interpolate between points to
    estimate an error.  Unfortunately, this may not necessarily be so.
    This became obvious to me on EBay in inspecting some certificates
    issued to late-model Hughes sextants by the British Navy that showed
    a continuous curve.  I don't recall the methadology used to generate
    the curves, if it was listed.  The curves were all over the place
    with substantial peaks and valleys occurring between fixed points.
    This, of course would be less of a problem with error determinations
    at 15d intervals than 30d intervals, but is still a potential
    problem.  Perhaps Mr. Morris will poke around with his calibration
    machine to test this hypothesis.  I would think the high end of the
    MkII scale would be a fruitful starting location.
    
    I'd also be curious to learn Mr. Morris' opinion of by how much one
    must undershoot a reading to reload the thrust bearing at the reading.
    
    Fred Hebard
    
    On Jan 13, 2008, at 7:21 PM, frankreed{at}HistoricalAtlas.net wrote:
    
    >
    > Two weeks ago, Bill Morris wrote about calibrating his sextants.
    >>
    >>
    >> "My 1981 instrument meets Alex's specification but not mine: 15d.
    >> +1"; 30d
    >> +1"; 45d +4"; 60d +7"; 75d +8"; 90d +11"; 105d +9"; 120d +8"."
    >>
    >> That's excellent.
    >>
    >> "My Mk II s/n 14176, 1942 in near-new condition with a certificate
    >> from Long
    >> Beach Shipyard dated 7 January 1986, does well too, except above
    >> 90 degrees.
    >> I give the original certificate figures followed in brackets by my
    >> own,
    >> which are each based on the mean of three careful readings: 15d
    >> +3"(+1");
    >> 30d -14"(-12"); 45d -17"(-16'); 60d -25"(-22"); 75d -30"(-31"); 90d
    >>  -33"(-40"); 105d -12"(-31"); 120d 0"(-30"). For most practical
    >> purposes
    >> except lunars, the differences are insignificant."
    >>
    
    
    
    --~--~---------~--~----~------------~-------~--~----~
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

       
    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