There were several threads last year which addressed the capabilities of the slide rule technology. A new book From Archangel to Senior Crown - Design and Development of the Blackbird by Peter W. Merlin of NASA published by the AIAA has some interesting comments on the state of computing technology at that time of the Blackbird development:
From page 9: "... Johnson and his team of engineers had to draw on available enabling technologies and design tools. Routine calculations were made with slide rules. More complex calculations, such as stress analysis, requuired Friden mechanical calculators. The most advanced computer available at the time was the IBM mainframe. ..."
From page 154: "... Perhaps the most impressive characteristic of the Blackbirds is the fact that they were designed before the advent of supercomputing technology. A small team of talented engineers, using slide rules and know-how, built a family of operational airplanes capable of flying faster and higher than any airbreathing craft before or since. ..."
From page 158: "... Although Pratt and Whitney had a very large computer system for its day it was no more sophisticated than some of the hand-held calculators that became available within two decades. Consequently, like the Blackbirds it powered, the J58 was essentially designed by slide rule.
We did have Fridens both at Honeywell and at Area 51. A few of the Fridens even had the square root capability. For trig funcions we had some truncated series but more often than not used lookup tables. In the olden days we carried our log log duplex decitrig on our belt and our Chemical Rubber book of log and trig tables under our arm.
Palmer