NavList:

Last week, Patrick Smyth asked:

Can anyone tell me how the first sight reduction tables were produced?

I believe the first edition (here in the UK) was in the 1930's with the looming war and the need for navigators being the driver for a simpler way to do the work. But how were all the calculations done, checked, and printed? Lines of people with mechanical calculators cranking away all day long? 

For others wondering, Patrick had contacted me via ReedNavigation.com, and I suggested he should post here since certainly there would be interest in this question. Unfortunately, his question seems to have been missed by most NavList readers. He added a little more detail in his earlier question to me so maybe I can add that he's interested in the publication of "modern" sight reduction tables. In other words, the immediate predecessors of Pub.249, 229 and similar tables. Tables like these originated just before the Second World War, as Patrick noted in his question. Gary LaPook posted some extensive messages on the general properties and history of some of those early tables. If I remember correctly from his earlier posts, the tables were created in the UK near the beginning of the war, and editions were published by the US Navy in a barter arrangement during the lend-lease years. Those tables became H.O. 218 which were published in sets covering every 5° of latitude in 1941. I have one in front me here. The title page is marked "Restricted" (low-grade "Classified"?) and the credit line on the title page of each volume reads "Reproduced by photo-lithographic process for emergency use from British Air Publication 1618" so those tables "1618" would presumably be among the earliest of the "modern" sight reduction tables.

Back to the question, how were they calculated and produced? I don't know any specific details (and hope someone else does), but we can count on certain features:

• rooms full of "computers" --people, often women, who did the number-crunching
• mathematicians who managed the calculation and created systematic operations for the computers (they wrote the spreadsheet, the "computers" were the cells of the spreadsheet).
• the best adding machines of the day.
• more rooms full of "differencers" --people who would check the calculations by differencing and second-differencing and probably higher-order differencing.

All of this would have been standard for many decades, and I would not be at all surprised if there were also analog computing engines (mechanical computers with gears) doing at least some of the work.

-FER