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: Calibrating a sextant: with a sextant and a spotting scope
    From: Bill Morris
    Date: 2011 Oct 8, 23:01 -0700

    I took a break from composing a blog post on chronometers to try out your method again, this time setting the sextants on a flat and fairly level surface and setting both frames horizontal to within a few minutes. I was then able to get repeatable results with a x6 telescope to within about 0.4 minutes using sextants whose errors summed to 1 second at 30 degrees and 3 seconds at 60 degrees. However, the individual calibration errors themselves had an uncertainty of maybe 3 seconds.

    Routinely, I cannot get repeatablity of index error to better than about 0.3 degrees, but I must try determining index error with a x26 theodolite 'scope some day.

    Your method seems well adapted to checking micrometer error, though as most makers do not quote it, it may be difficult to know which sextant has the error. Using an autocollimator I've just checked a 1978 SNO-T and the micrometer error does not exceed 2 seconds. It is undetectable at 8 points out of 12. A 1975 Plath sextant is nearly as good, with a maximum error of 2.8 seconds, not exceeding 1 second at 5 out of 12 points. A 1953 Plath had a maximum error of 7 seconds, still very good. This was the one with the bent frame that I wrote about on my web site (www.sextantbook.com). If you look at the blog in the "Chasing tenths of an arcminute" category, you will see that many sextants are much worse than this.

    Bill Morris
    Pukenui
    New Zealand
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]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