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    Re: Mary Blewitt vs M.J. Rantzen
    From: Hewitt Schlereth
    Date: 2011 Mar 13, 15:15 -0400
    Hi Paul -

    I believe Gary has personal experience with HO 218. I have volumes D (15° - 19° N&S) and F (25° - 29°  N&S).

    The nice thing is they're compact - 6.5"X10"X.75". They're obvious shortcoming is each covers only 5° of Latitude. Initial entry is for declination (whole number), with the pages for each declination thumb-tabbed. The print is large and crisp. They're well made - thick cream-toned paper, cloth bindings - so just as books-qua-books, they're lovely.  A pleasure to handle.

    The star treatment is really slick, though limited to 22 stars. I tried one for 2010 against my StarPilot and did get a 5NM difference. But I was extrapolating the correction table which ends for the year 2000.

    Hewitt

    On Sun, Mar 13, 2011 at 2:25 PM, Paul Werner <paul.werner{at}comhem.se> wrote:

    In CELESTIAL NAVIGATION FOR YACHTSMEN; 2nd ed. 1953, by well-known CN-author Mary Blewitt, the examples are based on A.P.1618/ H.O.218, A.N.T. Astronomical Navigation Tables. But as they soon were to go out of print the author strongly advises “… any yachtsman to get them while he can as they are ideal for yacht navigation”. And that in spite of an oddity: refraction included in the reduction tables.
    In 3rd ed. 3rd impression 1961 the change to A.P.3270/H.O.249, Sight Reduction Tables for Air Navigation, has been made. But the old A.N.T. are still described as “excellent” and “… as easy to use and a good deal easier to read, as well as being smaller, than A.P.3270”.

    Another CN-textbook author of that time, M.J. Rantzen, is not that enthusiastic. In his book LITTLE SHIP ASTRO-NAVIGATION; 1952, the reader is warned: “In short, A.N.T. should not be used for single or double sights unless the navigator is prepared to accept a possible unknown position error of, say,5 to 10 miles or thereabouts”. The refraction inclusion is also mentioned as a drawback.
    The little ship navigator is recommended to use H.O.214, if available, without bothering with the t an L corrections. And as “standby” use the cosine-haversine method. A.P.3270/H.O.249 tables are not mentioned at all unless I missed it.

    Question:
    Mary Blewitt - too incautious, too careless (can that be possible?) or M.J. Rantzen – exaggerating?

    And:
    If M.J. Rantzen’s warning is motivated for A.N.T., is it valid for A.P.3270/H.O.249, the Rapid Sight Reduction Tables of today, as well?

    Paul Werner

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