A 1950s vintage Hughes-Owens Model 1771 slide rule used for many scientific calculations. This version, which measures 30 cm in length, came complete with a protective leather case. The first handheld scientific calculator, the HP-35, was introduced to the public by Hewlett-Packard in 1972 and quickly replaced the slide rule. Until that point most scientific and engineering calculations that required no more that three-digit accuracy were carried out using slide rules. Slide rules, whose principle of operation is based on logarithms (logs for short), allowed rapid multiplication and division operations. The Model 1771 model was a fairly basic model – physically larger models allowing higher precision and often produced with more scales to extend the types of calculations to those including geometric functions such as sines and cosines (and others) were also made.
