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    Re: Sight Reduction method accuracy
    From: Henry Halboth
    Date: 2004 Apr 4, 15:34 -0400

    Thought I might add something regarding the comparative accuracy of the
    various sight reduction methods spoken of here from time to time.
    
    Over the years, I have experimented under all conditions at sea with most
    methods, at least through HO 249 - specifically this is meant to include
    the Longitude Time Sight, Marc St. Hillaire, Ageton, Dreisenstok,
    Martelli, several British Admiralty methods, HO 214, and HO 249 - and
    never found any significant discrepancy as respects positions found, with
    the possible exception of HO 249 in the use of which "rounding off"
    errors seemed to tend to multiply and result in more than the usual
    number of "cocked hats". As a matter of convenience, especially in
    cramped small vessel navigation, I favored Dreisenstok (HO 208) over most
    other methods and could match speed of calculation, as well as accuracy,
    with most any other method - for pre-computation of altitude and azimuth,
    I found HO 249 a handy accessory tool.
    
    I became at one time enamored with (and still am) Martelli's Tables which
    constitute one of the first short tabular methods for solution of the
    Longitude Time Sight, although in recalculating, I have found several
    errors or misprints in my copy. These tables are simple and easy to use,
    and with a little manipulation can serve for intercept calculation.
    Unfortunately they do not provide for the computation of azimuth, for
    which other tables or formulae must be employed.
    
    As respects the age old discussion of utilizing a DR position, as opposed
    to an assumed position, in any intercept method, there never seemed to be
    any significant or practical difference in positions established by
    whatever method was used. This of course does not refer to utilization of
    the Time Sight solely for longitude, in which case an accurate Latitude
    must be employed - the more so as the body moves out of the prime
    vertical toward the meridian.
    
    Someday I will share with you my experience with Lunar Distance
    observations at sea, which date back to the 1940's before the apparent
    current renewal of interest.
    
    Regards.
    
                                            Henry
    
    
    

       
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