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    Re: Sight reduction methods
    From: Gary LaPook
    Date: 2015 Nov 4, 01:11 -0800

    I wrote this back in 2011:

    Re: Evaluation of H.O. 218
    From: Gary LaPook
    Date: 2011 Mar 24, 22:25 -0700

    I give em an "A". The second part of the tables is exactly like H.O. 249 volumes 2 and 3 so if you like using them and the accuracy is sufficient for you then H.O. 218 makes a very compact substitute. The selected star section is just as easy to use. The altitudes in both sections are limited to 10 to 80 degrees, no low angle and no very high angle shots. The Hc values include the refraction correction so you do not have to apply this correction to sextant altitudes. The correction is based on an altitude of 5,000 feet but are virtually the same as at sea level so the tables can be used as-is. All the "t" corrections stay the same for a whole year so you can just make a note of them for the current year so no need to always look up a correction in a multiplication table as when doing "delta d" for stars with H.O. 249 volumes 2 and 3. The books themselves are very compact. If your sailing is limited to a small range of latitudes say 15 or 20 degrees (which is true for most of us)  then the three or four volumes take up very little space. If you want to cover all latitudes then the entire set takes up more space than H.O. 249.
    One more advantage of H.O. 218 over H.O. 249 volume 1 is that it can be used for a very long time, 70 years so far, so you don't need to buy a new volume 1 every 5 years.
    gl

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    Re: Sight reduction methods
    From: Stan K
    Date: 2015 Nov 3, 20:08 -0500

    Gary,
    I have a Volume J (latitudes 40º-44º) of HO 218, but I have never played with it.  I didn't acquire the book (at a used book store) until well after we discussed 218 here back in 2011.  Was 218 ever popular for marine navigation?
    Stan
       
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