When I tried to use my friend, Marion’s, calculator I quickly realized I had made an assumption that all calculators worked the same. Alas, I fell victim to a common assumption with computing machines–that they all work the same. At home my Mom had an HP calculator; Marion, my classmate, possessed a TI calculator. While they both performed addition, subtraction and even a square root, you did not use the them the same. So I skipped using a calculator, (which Mrs. Marcou had described as a “nice to have,”) and I proceeded, using manual techniques to pass the math exam on limits.

When I started Algebra II Trigonometry, we soon reached the topics of logarithms and trigonometry. Translating the functions into numbers could be done a number of ways: tables in the back of the textbook, calculators (new,) slide rules (old school.) Using the tables could sometimes involve interpolation and extrapolation. Calculators had started to appear on the scene; however, the high school curriculum did not yet require them. After showing me how to use it, Dad lent me his slide rule to take to high school.

In the classroom, I dutifully took it out to calculate a value. Upon seeing my actions, Mrs. Marcou suggested that I leave it at home. I vaguely recall a remark that it was old-school and that I needed to update my technology.

Alas, while I could use Mom’s HP calculator at home for math homework, I could not bring it to school. Dad gave Mom the calculator because she loved mathematics. As a substitute teacher for Montgomery County School system, she was in high demand. She could walk into a math class “cold” and teach the subject. I never heard the words “Math is too hard for girls.” In fact, I suspect that Mom out-calculated Dad when it came to higher mathematics; and Dad worked as an engineer.

Now back to that math exam: when Mrs. Marcou stated that we could use a calculator for the exam on limits, I asked Marion to borrow hers. Little did I know that the TI calculator used XX algebraic and the HP calculator used Reverse Polish. The subtle difference can be illustrated with 2+2:

TI: 2 + 2 =; 4 appears

HP: 2 2 +; 4 appears

Why would calculating require a different order the numbers and operands? My 10^{th-}grade mind had not a clue. And in the midst of exam stress I had no time to decipher the working of the TI machine. So I went back to the techniques that Mrs. Marcou had presented in class. Turns out I really didn’t need that calculator to pass the exam.

Have a productive day,

Anne Meixner

Dear Reader, what memory does this piece spark in you? Do you have an equipment/operator failure story? Please share your comments or stories. You, too, can write for the Engineers’ Daughter–see “Contribute” for more Information.

Additional Reading

There happens to be a Slide Rule Museum.

Watch this video for log and trig calculations on a Slide Rule.

A little bit on Reverse Polish

Article on why HP engineers used Reverse Polish.