The Slide Rule
Besides the ball point pen, there was another article I had to buy at the Rhode Island State College book store. Anybody who took physics or college math was required to acquire and learn to use a slide rule. All engineering students had to have one and they usually bought the best, which at the time was made by Keffel & Esser. I had to have the best and so that's what I bought, along with a case for the same. Cost me a big $37. This allowed men students to hang the article from the belt and thus be in sinc wih all the other nobles of the quadrangle.
Now, if you knew the ins and outs of the slide rule you could do rapid calculations of trigonometric functions in addition to obtaining the product of other mathematic computations. Of course, you had to move the slide rule and cursor to the proper location if you were to get the correct answer to the problem. This took a little skill along with patience and lots of practice.
A person can now obtain a simple calculator in just about the same way as in obtaining a ball point pen. The AARP and AAA always seem to have something going that permits a person to get a good calculator... free. And, if not free then one can buy a simple calculator for two or three dollars. If a scientific calculator is needed then the cost is just a little bit more. But what you can do with these instruments is so much easier and so much more accurate than what you can do with slide rules, which have gone the way of buggy whips.