My 1st Computer "The Slipstick"

Before the pocket calculator became popular and economical, the slide rule (sometimes called a slipstick) was the commonly used calculation tool for scientists and engineers. Their use continued until about 1975 when Hewlett-Packard introduced pocket calculators for under $50.00

A good history and explanation of how to use a slide rule can be found in this Wikipedia Link.

My first slide rule, which I purchased my freshman year in college (1958) for about $25, was the Post Versalog Model 1460. This is the classic bamboo slide rule. It was manufactured by the Frederick Post Company. It came with a hard leather case, belt loop and a metal hasp on the belt loop. This slide rule was also a good humidity indicator. Being bamboo, it tended to swell in damp weather and the slide could become to tight to operate. Here are the front and back views of the Post Versalog.
Today a Post Versalog Model 1460 can still be purchased on eBay- cost range of $10-70 based on quality.

Without a slide rule the other method of doing scientific calculations was the use of logarithms. I remember using logarithms to do multiplication-division calculations in freshman chemistry.

When I started to work as a chemist for Petrolite Corporation in June of 1966, the company issued me a slide rule. It was a plastic 12 inch Acu-Math Model 400B.
I also have a 7 inch plastic pocket Acu-Math Model 1240.
I also have an aluminum 6 inch Pickett Model 600 pocket slide rule.
Here are the front and back views of the Pickett 600.
I have a pocket circular slide rule that was provided by one of my equipment vendors.
This slide rule had handy slide out conversion tables for such units as mass, volume, velocity, flow rate and pressure along the periodic table of elements and temperature conversion chart on the back.
I can remember when one of the groups in my company bought a HP10 calculator for everyone in the group for $100 each. These were a basic 4 function calculator (multiplication, division, addition, subtraction) . Today a basic 4 function calculator is a give away item the size of a credit card.

I still have the calculator that I used at work, the Texas Instruments programmable TI-66.
Even though slide rules had gone almost completely away by the 1980's, I can remember colleagues (engineers) that still had to carry a slide rule in their pocket.