HP HP-21 - Page 32

30 How the HP-21 Works
Now 34 and 21 are sitting vertically in the stack as shown
below, so we can add.
T 0.00
Z 0.00
Y 34.00
X |21 Display.
Press Display
The simple old-fashioned math notation explains how to use
your calculator. Both numbers are always positioned in the
stack first; then the operation is executed when the key is
pressed. There are no exceptions to this rule.
The answer.
Subtraction, multiplication, and division work the same way.
In each case, the data must be in the proper position before the
operation can be performed.
To subtract 21 from 34:
34
-21
Press Display
34 34 is keyed into X.
34 is copied into Y.
7 EZ:_—_J 21 writes over the 34 in X.
[ The answer.
To multiply 34 by 21:
34
x21
Press Display
34 34 is keyed into X.
34 is copied into Y.
21 21 writes over the 34 in X.
(x] The answer.