Terminated: 1983
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
followed by
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 exponent, otherwise it will enter the constant π.