Brand: CASIO
Model: COLLEGE fx-81
Type: Scientific calculator
Picture: CASIO fx-81
Batteries: AA x 2
Lifetime: Introduced: 1981
Terminated: 1983
Notes: The CASIO fx-80 and this one, the CASIO fx-81 were the most popular calculators when I myself was still in high school. It has all the basic scientific functions, and ran for ages on its two AA batteries.

CASIO fx-81 display The CASIO fx-81 was cheaper than the CASIO fx-80 because it officially doesn’t have statistical functions. That was a little trick of CASIO because these two calculators were technologically exactly the same. To enter the statistical mode on the CASIO fx-80 one has to press "INV" "D·R·G". When these keys are pressed on the CASIO fx-81 the display shows "ERROR", as shown here, at the position where the CASIO fx-80 shows "sd". However, all statistical functions are there, it’s just a matter of remembering the CASIO fx-80’s key layout! The "ERROR" notification is just there to scare you. I was quite surprised when I found out at the time. The CASIO fx-81’s manual warns that, if for some strange reason this ERROR message is shown, one should switch off and on the calculator to clear it! Quite interesting how this works as a business model.

One of the disadvantages of this calculator and the CASIO fx-80 is that its power slider wears out rather quickly. Easily fixed by bending the contacts and cleaning them. I was the guy in the classroom that could do that!

This calculator (as do many other CASIO scientific calculators) uses one and the same key for both the constant π as well as exponents. This works as follows. When you first enter digits, the "EXP"-key will enable you to enter the numbers exponent, otherwise it will enter the constant π.