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: Lunars with SNO-T
    From: Alexandre Eremenko
    Date: 2004 Oct 28, 13:14 -0500

    Dear George,
    I am surprised that that one rejected distance in
    my first lunar triggered so much exchange.
    I think this is based on some misunderstandings,
    and maybe my statements in this exchange were not clear
    Let me begin with two statements which I want to make
    completely clear:
    1. What does it exactly mean: "rejected an observation".
    I did not erase it from my log. When necessary I reduced it
    too and the result is kept in my log.
    The purpose of computing and reducing the average is to
    obtain the "final result", let's say, my chronometer correction.
    I want my chronometer correction to be as close to the TRUTH
    as possible. Could I make any use of this "rejected" distance?
    Yes, I could. When I would judge about the likely error
    of my observations, I WOULD take it into account.
    But to compute my chronometer correction I decided to reject it.
    The later reduction of rejected distance PROVED that
    for this particular series I was right:
    rejecting this observation improved the average.
    2. In my explanation why I rejected it, I did not mean to
    formulate any general rules for rejection.
    I rejected it using my common
    And then, when asked, tried to analyse and explain how my
    common sense worked in this particular case.
    If I am asked to state a general rule for rejection, the
    only rule would be:
    Now let me comment some points of your message.
    On Wed, 27 Oct 2004, George Huxtable wrote:
    > I ask him if he can quote any authority in support
    > of such a dogmatic attitude.
    The only authority is my common sense.
    I repeat this is not a dogmatic attitude:-)
    The statement was nor a "rule", not a "dogma", but
    an attempt to explain how my common sense worked in this
    particular case.
    > Pursuing this matter, I have asked whether the rejected point in his first
    > lunar set would still have been rejected if the discrepancy had been an
    > arc-minute less-
    Such questions can be asked to infinity:-)
    When my son was 4 years old I told him that the highest
    mountain is Everest. His next question was: "What is the lowest mountain?"
    I tried to explain him why this question has no reasonable
    answer. Do you really want me to repeat this explanation
    on this list?
    > That shows a welcome flexibility creeping in, but the picture I get is that
    > Alex is very reluctant to abandon his self-imposed rule.
    I repeat: the only "self imposed rule" was:
    use common sense. (This rule I will never abandon:-)
    Again: I never wanted to claim that EVERY deviation from monotonicity
    has to be rejected in EVERY set of data.
    And sorry if my statements could be interpreted like this.
    I was talking of THIS PARTICULAR series, nothing else.
    A question to George:
    Suppose you are in Sea, have no radio, and taking lunars
    to compute your chronometer correction.
    And you obtained exactly that series of lunar distances I had.
    How would you proceed? Would you average all 6 or reject one?
    > Finally, I asked Alex this question about his second set of lunars-.
    > be interesting to know exactly what were those averaged values that were
    > fed back into Frank Reed's program, and whether any rounding had taken
    > place.
    Those averaged values were given in my observation reports: In the first
    report: AVERAGE GMT: 4:13:13 AVERAGE DIST: 23.54' In the second report:
    AVERAGE GMT: 0:26:28
    AVERAGE DIST: 70d41.0'
    They were rounded to 1 sec of time and .1' of distance.
    Which I always do, of course: if the almanac itself does it,
    what is the point of messing with extra digits myself?
    > So there's no
    > discredit to Frank's program.
    Who was talking on "discredit"???
    Of course, his program also does rounding, how else can it be??!

    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