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    Re: Berson's Noon Sun problem
    From: Stan K
    Date: 2013 Feb 12, 21:24 -0500
    Robin,

    Glad I was able to relieve some of your frustration.  (Did I just say that?)

    Regarding the H.O.249 "accuracy", I have to admit that I never thought about it this way, and it makes a lot of sense.  I'm embarrassed to say that I simply did it the way I was taught, without a second thought.  However, I can say with certainty that I have never seen H.O.249 done with intercepts with better than 1 nm resolution.

    Stan


    -----Original Message-----
    From: Robin Stuart <robinstuart@earthlink.net>
    To: slk1000 <slk1000@aol.com>
    Sent: Tue, Feb 12, 2013 7:04 pm
    Subject: [NavList 22344] Re: Berson's Noon Sun problem


    Stan,

    Thank you for posting this. It’s great to get confirmation of my calculation of the intercepts for the March/April 2012 and October 2012 problems that had caused me so much frustration. I was also thinking contacting Ocean Navigator and pointing out the errors but if they are unresponsive I wont bother.
    One comment that I have is that I do think that there is value in retaining the decimals of a minute when calculating the intercept even when H.O.249 is used provided that you also keep track of the actual errors associated with the result and don’t interpret 6.7nm to mean that it is accurate to +/-0.05nm.

    To be specific, in the October 2012 example H.O.249 gives a calculated altitude at the AP of 46d15’. There will be a possible error of +/-0.5’ from the main table and +/-0.5’ from the interpolation table yielding a total of +/-1’. We then know for certain that the true value of the altitude Hc lies somewhere between 46d14’ and 46d16’. Ho is 46d21.7’ with a much smaller error and we know that the true intercept, Ho - Hc, lies between 5.7nm or 7.7nm and so we should interpret the intercept from H.O.249 as (6.7+/-1)nm but definitely not (6.7+/-0.05)nm as the significant figures might imply. Rounding to 7nm would suggest an intercept of (7+/-0.5)nm which actually overstates the accuracy and if I were to write the intercept as (7+/-1)nm I don’t match the true range of values in which the intercept could actually lie.

    Regards,
    Robin
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