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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: H.O. 203/204, Littlehales, Hydrographic Engineer
From: Henry Halboth
Date: 2017 Mar 23, 01:09 -0400
You will undoubtedly recall that on 11/11/15 I posted a blurb about HO 203 & 204  which included  a reworking of some previous sights to demonstrate their use and relative accuracy. Although these posts generated little or no comment at the time thez remain in the archives and maz be referenced if so desired.

Henrz
Please excuse the misspellings  mz computer has decided to print y  for z again or vice versa.

On Wed, Mar 22, 2017 at 11:48 AM, Brad Morris wrote:
Bob

Yes, there is specific interpolation assistance!

For each dependent value of Hour Angle, there is an increment provided for each 1' of change in declination.  Similarly for azimuth.

The dependent Hour Angle is a function of the true altitude, given generally in 1° steps.  The interpolation assistance is for each 1' change in declination.  That is, the dependent hour angle changes as the independent variable (declination) changes.  So as we look up, using a whole number for Latitude, a whole number for Declination and a whole number for true altitude, we obtain dependent values Hour Angle and Azimuth.  Those values are changed by each 1' of additional Declination from the whole value used in the lookup.

I certainly surrender on the point of primacy.  I wonder why Littlehales did not reference that prior text?  One wild guess: it took time to create tens of thousands of entries for 1600 pages and check them.  Perhaps HO 201 didn't exist when Littlehales conceived of the table, but 201 beat him to print???  That is a total guess, and again, I cannot support it.

On Mar 22, 2017 10:25 AM, "Robert VanderPol II" <NoReply_RobertVanderPolII@fer3.com> wrote:

It sounds like this may have been the 2nd inspection table as opposed to mathematical tables like Weems, Driesenstock or Ageton.

My 1984 edition of Bowditch lists HO-201 (1919,Simultaneous Altitudes and Azimuths of Celestial Bodies) which it describes as a lookup table.  606pg, Lat to 60o, Dec to 24o, LHA tablulated every 2.5o.  It comments that the tables were well arrange but no assitance was given for interpolation of declination.  Based date and HO number this appears to pre-date 203/204.  Does 203/204 give interpolation assistance?  The expanded range explains the table growth.

Thanks for the info.

Bob II

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