Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: Bris Sextant Calibration
    From: Francis Upchurch
    Date: 2016 May 24, 19:00 +0100

    Thanks both.

    Great method.

    Just invented same(thought I was clever but as usual, I’m generally second!) to compare my  lovely  Francis Barker little  Box  sextant with my trusty Astra B which for many years has been perfect.

    Method works. (Box sextant pretty good considering size etc. Well +/- about 1-2’ arc max, usually better compared to Astra which is spot on). Hope to use the Box sextant to re-enact some of the Chichester stuff later, if my poor ship, recently crushed by a 500 ton cargo vessel ias repaired on time.(Cornish have a word “directly” meaning any time soon or maybe in the next hundred years. Bless them. It is one reason I chose to live down here after escaping from the madness of London.



    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Frank Reed
    Sent: 24 May 2016 18:39
    To: francisupchurch@gmail.com
    Subject: [NavList] Re: Bris Sextant Calibration


    Greg Rudzinski, you wrote:
    "It is a great deal simpler to compare sextant to sextant directly. No timing, sight reduction, or trips to the beach. The Bris can now be calibrated in the back yard. "

    Yes! Very nice. I've written on something quite similar before... If you take any two sextants and set them to the same angle, and then set them on a table index mirror to index mirror (some fiddling around required but it should be obvious), then the test for calibration reduces to a plain index error test. The idea here is that the well-calibrated instrument "feeds" light which is already deflected by the angle showing on the arc to the second instrument. The second instrument takes out that deflection if it is set to the same angle. Then you line up some very distant object in both reflected and direct view (just like an index error test). Any difference on the displayed angle on the second instrument is the calibration error of that instrument. Naturally this won't work unless the calibration of the first is reliable. It's a method for transferring calibration from one sextant to another. It will work with a Bris as easily as a Davis ...or a Tamaya ...or an Astra.

    Frank Reed
    Conanicut Island USA

    View and reply to this message

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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