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Re: B-II Celestial Computer & Three-Minute Adjustments
From: Joe Plazak
Date: 2025 Feb 22, 18:46 -0800

Thanks to everyone for their helpful replies on this thread, and special thanks to Murray for tracking down the edition of the AFM 51-40 that described the B-II computer.  Very cool!  

Murray- I would be very interested in reading the subsequent pages (if your time allows for a few extra photos).  

As for the "three-minute adjustments," I found a clue in the FAA-H-8083-18 Flight Navigator Handbook.  In the chapter on "Special Celestial Techniques" (Page 12-8), the book describes "Eliminating Motions with the Bracket Technique."  Interestingly, they write:  

"For sun observations, you can eliminate motion calculations by using a shooting schedule of 3 minutes early, on fix time, and 3-minutes late. With this schedule, the 3-minute early and 3-minute late shots have the same magnitude of motion but an opposite sign. Therefore, these motions cancel each other out and do not need to be computed. The on-time shot has no motions. Therefore, the three intercepts can be averaged for a single LOP."  

Perhaps that is why the SAC was advocating a three-minute shooting schedule?

Then, directly below (on the same page), the handbook details modifying a DR computer so that it can be used for quick and accurate "combined" (i.e., body and observer) computations of 1 minute motion adjustments!  Snippet attached.  I'm going to make that modification and compare the results against the Polhemus computer.  It sounds too easy. 

-JP

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