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Absolutely fascinating stuff you posted. Many thanks to you and others involved. While slide rules were and still are fascinating, I never used them much during my career, such as it was, Piping Design and Fabrication. Trig. calculations can certainly be done with a slide rule, stick or circular, however since we had to give fabricators all dimensions to 1/16", the trig. calculations involved could not be done on a slide rule. Prior to electronic calculators, we used Smoley's Tables, nowadays an antique, or possibly a paper weight.Who knows, there might even be reference to them in some dark corner of The Internet, I never bothered to look. I will peruse through the material you posted, possibly learning something in the process. In any case, thanks much for your efforts.