A group of engineers were discussing old ways of calculating things and the slide rule came up. Engineers used slide rules to multiply, divide and calculate roots of numbers. Slide rules used logarithmic scales. Bob Hannon of JHU/APL put together a good presentation on the history of slide rulers.
H-P introduced the HP-35 calculator in Feb 1972. Slide rules rapidly become obsolete. The electronic calculate then laid the groundwork for the personal computer. The first complete personal computer was the Commodore PET introduced in January 1977. It was soon followed by the popular Apple II and then the IBM personal computer (PC).
Slide rule information
www.sliderulemuseum.com has an excellent tutorial on how to use a slide rule, with an on-screen slide-rule simulator if you don’t have your own slide rule.