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: Systematic error and its resolution
    From: Geoffrey Kolbe
    Date: 2007 Apr 06, 21:39 +0100

    Alex, the index error of a bubble sextant can be determined from an unknown
    By taking sightings on bodies in opposition, the separation of the
    resultant position lines will, on average, be twice the index error.
    In my posting #2531, I advocated taking four sightings, a North-South pair
    and an East-West pair, on bodies at the Cardinal points. The North-South
    pair effectively give you your latitude and the East-West pair your
    longitude. The position lines from the four sightings should form a square
    box if index error is the dominant error. If the box is not substantially
    square, there is a non-systematic error somewhere which is of the same
    order or greater than the index error.
    See http://www.pisces-press.com/desert/14thMarch.jpg for an example of what
    I mean. In this example, the box is substantially square, giving us
    confidence that the dominant error is indeed index error. The size of the
    box is about 10' on a side, from which we deduce that the uncorrected index
    error was 5'. The position lines are all 'away from' the body in question,
    so the sextant altitudes are 5' too small. I need to add 5' to my altitudes
    to correct the index error.
    A subsequent round of sights at a different location a few days later show
    the results when this 5' is factored in. See
    Geoffrey Kolbe
    At 20:24 06/04/2007, you wrote:
    > > It is easy to determine the Index Error of a marine
    > > sextant, but not of bubble sextants.
    >Easy or not, but I infer from your message that you
    >can find the IC of your bubble sextant SOMEHOW.
    >I don't see any way to do this at all,
    >except taking an altitude from a known position.
    >This can be done once in a while, but certainly not
    >before or after an observation, if the purpose of
    >the observation is to find this position.
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com

    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