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    Re: Versions of Dreisonstok, H.O. 208
    From: Robert Pearson
    Date: 2017 Mar 3, 12:33 -0800

    Peter,
    I have a copy of the H.O.208 5th Edition dated 1940.
    Latitude in Table I goes from 0 to 65 deg. "t" goes from 0 to 90 deg across the top of the pages.
    There is no Table I-A.
    (d+b) in Table II goes from 0 to 89 deg across the top of the pages with minutes 0 to 60 down the left hand side and from 90 to 179 deg across the bottom and minutes from 0 to 60 up the right hand side.

    I have a copy of H.O.208 6th Edition dated 1942.
    Latitude in Table I goes from 0 to 65 deg. "t" goes from 1 to 90 and 270 to 359 deg across the top of the pages and from 90 to 179 and 181 to 270 deg across the bottom.
    Table I-A extends Table I to include latitudes from 66 to 90 deg.
    (d+b) in Table II goes from 0 to 89 deg across the top of the pages with minutes 0 to 60 down the left hand side and from 90 to 179 deg across the bottom and minutes 0 to 60 up the right hand side.

    I have 2 copies of Letcher's "Self Contained Celestial Navigation with H.O. 208" both dated 1977. IIRC only 1 edtion was ever published. The reprint of H.O.208 6th Edition in them matches the format of my copy of H.O.208 6th Edition dated 1942.

    I also recall some scanned digital editions I found on-line but that will take some time to find where they are. I don't know what edition or date they are without searching for them.

    You posted:

    The edition 5 (and presumably earlier editions) with no angles past 90 in Table 2 is particularly challenging if you are not mathematically inclined, and not helped in the least by the incorrect instruction as to how to handle a (d+b) value greater than 90. The instructions say to take 180 - (d+b) and use that to find the correct column... but that instruction is wrong. You take 179 - (d+b) because each column has increments to 60 arc-minutes that make up the rest of the remaining degree. You also must reverse the arc-minutes to read form 60 at the top to 0 at the bottom for this to work which is not metioned at all in the instructions. If you were not holding the other versions in your hands you would likely be misled by those incorrect instructions.


    I don't agree with your comment here. The instructions in H.O.208 are correct. For b+d greater than 90 take 180 - (d+b). If Table II goes from 0 to 89 deg across the top and from 0 to 60  minutes down the side then the angle or it's suppliment is the correct value to enter the table with. Table II is merely a table of log cosecants and log cotantents. Using 179-(d+b) to enter this table won't give the correct values for B and D.

    I suggest you check this by comparing results for Table II 6th Edition against Table II 5th Edition for say b+d = 93° 10'. In the 6th Edition reading 93° at the bottom of the page and 10' on the right side I got B=66, D=8743. Then use the supplement of this angle, 180-93° 10' = 86° 50', to enter Table II 5th Edition. Entering with 86° at the top of page and 50' at the side I read B=66, D=8743.


    Robert Pearson

       
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