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    Re: Intercept method
    From: Doug Royer
    Date: 2003 Jun 23, 13:01 -0700

    Bill,actually in real life I would not looking for this great degree in
    accuracy.I understand what you say about the hand held sextant.I did this
    experiment only because it looked interesting.I expected the results
    obtained by the intercept method to be a closer match to the results
    obtained by other methods.I know that on 06-21 thru 06-22 my chrono was 1-2
    sec. slow and the mer. pas. solutions closely matched the actual error where
    the intercept method was not close.I can say I will most likely not use
    Lunars to check errors or time as other methods are as or are more accurate
    and easier to do.At the least I am familiar with the procedures in case I
    ever need them.Thanks for your input.
    -----Original Message-----
    From: Noyce, Bill [mailto:william.noyce@HP.COM]
    Sent: Monday, June 23, 2003 11:47
    Subject: Re: Intercept method
    Doug, I haven't tried to follow your numbers, but my initial
    reaction is that *no* lunar method with a handheld sextant can
    be expected to give the kind of precision you seem to be looking
    for.  Remember that it takes roughly two minutes of time for the
    moon to move one minute of arc against the fixed stars (at best
    -- sometimes it moves quite a bit more slowly).  This means that
    to achieve a precision in time of 6 seconds (0.1 minutes of time)
    you must make your observations to a precision better than 0.05
    minutes of arc (3 arc-seconds).  For the intercept method, I
    believe you must achieve this precision or better for all the
    altitudes that feed in to the problem.
    Lunars can check your chronometer to within a minute, or perhaps
    a bit better.  If you can consistently get results within 10
    seconds, especially using the intercept method, I'll be surprised.
            -- Bill
    -----Original Message-----
    From: Royer, Doug [mailto:doug.royer@REMEC.COM]
    Sent: Monday, June 23, 2003 2:27 PM
    Subject: Intercept method
    I tried again over the weekend to work the Lunar intercept method as
    explained by Mr. Umland.For the 2nd time in as many attempts the results are
    questionable.Are they questionable because of mechanical errors of the
    sights,errors in reduction methods or errors in the interpretion of the math
    from chapter 7 of Mr. Umland's papers?
    I don't believe it to be errors in the mechanics of the observations.Great
    care was taken to assure accurate observations and equipment.I don't believe
    it to be errors in reduction methods as 3 differant reduction systems were
    used to check the results.The sin-cos method useing a Casio fx-6300
    calculater has the Moon's intercept at 0.5 m A,Mr. Umland's Moon sight
    software has the intercept at 0.3 m A,the Admiralty's reduction software has
    the intercept at 0.4 m A.
    I believe I am not useing the intercept formula properly or it is flawed.I
    got a chrono error of  5.9 sec. slow useing the intercept method.Knowing my
    chrono was not that slow I set up and checked the chrono's error useing
    equal altitudes.The chrono error thus obtained was very close to the actual
    known chrono error.
    Mr. Umland's Moon and Sun reduction software is nice to use and has features
    I've not seen on other software such as getting the intercepts directly from
    the readings from a bubble sextant or artificial horizon.Times are Zd + 7.
    GPS pos. = 32*53.05'N,114*49.90'W
    06-22-03 030311 3 star fix AP = 32*53.2'N,114*49.7'W
    06-22-03 031439 Moon UL Hs=23*13.4',Ho=23*46.8',Hc=23*47.3',I=0.5 m
    f=-0.7348,delta T"=-5.93 sec. Chrono error is 5.9 sec. slow.
    Equal altitudes chrono error
    Antares Hs=58*34.2' at 221444 on 06-21 and 000303 on 06-22. 240303 +
    221444/2 = calculated Antares mer. pas. at 230854.Mer. pas. Antares at
    114*49.90'W = 230853.Chrono is 1 sec. slow.
    Sun LL at Hs=109*51.0' at 100700 and 151536 on 06-22. 100700 + 151536/2 =
    calculated Sun mer. pas. at 124118.Mer. pas. Sun at 114*49.9'W =
    124117.Chrono is again 1 sec. slow.
    What am I not seeing or doing correctly with the Mr. Umland's Lunar
    intercept method?

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