NavList:

David Pike, you wrote:  “Instructions or identifying which knobs moved which counters would be useful”.  I must say that Clint Crawford’s post sparked my interest in this fascinating device, as it reminded me that I had seen it in the Smithsonian Institution a few years ago. In an internet search I found a document that might answer your questions, and which I hope Clint Crawford will find of interest. This document is TM 1-206, the US War Department’s Technical Manual on Celestial Air Navigation, published on March 1941, and classified as “Restricted” at the time. The whole manual is available digitized (or digitised, if you prefer) in Google Books, and may be downloaded at no cost.  I’m attaching the nine pages which describe the Fairchild-Maxson LOP computer, and contain instructions for its use (Section 51, in the chapter “Reduction of the Astronomical Triangle”, pp. 94-102).

It’s interesting that this manual devotes quite a few pages to an instrument that was quite rare at the time of publication, and which was to remain so indefinitely; perhaps the authors assumed that it would become generally available. Your assumption regarding azimuth output is correct: though the computer was designed to solve for lines of position, one of its limitations, as stated in the last line of this document is that it “will not yield azimuth directly”. Another one, perhaps more alarming, is that it was “subject to mechanical failure. To recognize derangement, especially when the error is small, requires a thorough knowledge of celestial navigation.”  This remains true for all "black box" solutions to any problem still.

Best, RafaelC