Today in 1976, Keuffel & Esser produced its last slide rule, presenting it to the Smithsonian Museum.
The Reverend William Oughtred invented the slide rule around 1622 by placing two sliding wooden logarithmic scales next to each other. It was portable, easy-to-use and didn’t even required knowledge of logarithms. In “When Slide Rules Ruled,” Cliff Stoll quotes British mathematician Augustus De Morgan saying in 1850: “For a few shillings, most persons might put into their pockets some hundred times as much power of calculation as they have in their heads.”
This is exactly what happened, on a much larger scale, with the invention of electronic hand-held calculators. IEEE History Wiki:
Slide rules were simple mechanical devices used by engineers to multiply, divide, and perform other calculations that are based on logarithms and trigonometric relations. Keuffel & Esser and Pickett were the most common brands.
One of the most significant advances of the 20th century was the replacement of mechanical and electromechanical devices with electronic devices… pocket calculators initiated a dramatic change in the engineering community, as engineers discarded their beloved slide rules for the greater precision of electronic computation.
The HP-35 was introduced in January 1972. Named for its 35 keys, it performed all the functions of the slide rule to 10-digit precision. The HP-35 was 5.8 inches (150 mm) long and 3.2 inches (81 mm) wide and said to have been designed to fit into one of HP’s co-founder William Hewlett’s shirt pockets.