The Stack

The calculator can remember up to four last answers. It has four special memories for these and the set is called the "stack". The bottom of the stack has the latest answer. HP call this the "X register". The latest answer is what you see in the display. The answers from the last three calculations you did before that aren't normally displayed, but they are still remembered by the calculator in case you need them. They are stored in what HP call the "Y register", the "Z register" and the "T register". "T" is short for top. It looks like this:

T	0.00
Z	0.00
Y	0.00
X	15.00

You see this as:

15.00

One Number Functions

A one number function works like this:

T	0.00
Z	0.00
Y	0.00
X	45

T	0.00
Z	0.00
Y	0.00
X	0.71

The answer (0.71) replaces the X value (45).

Two Number Functions

A two number function works like this:

T	0.00
Z	0.00
Y	0.00
X	50

T	0.00
Z	0.00
Y	50.00
X	50.00

T	0.00
Z	0.00
Y	50.00
X	25

T	0.00
Z	0.00
Y	0.00
X	2.00

Normally, if you key in a number, any old answers get pushed up the stack. (The exceptions are after pressing CLX (clear X) or ENTER. With those two exceptions, the keyed in number replaces the (cleared or entered) number in X.)

Complicated Equations

A complicated equation works because the stack remembers answers like this:

T	0.00
Z	0.00
Y	0.00
X	9

T	0.00
Z	0.00
Y	0.00
X	3.00

T	0.00
Z	0.00
Y	3.00
X	2

T	0.00
Z	3.00
Y	2.00
X	2.00

T	0.00
Z	3.00
Y	2.00
X	3

T	0.00
Z	0.00
Y	3.00
X	5.00

T	0.00
Z	0.00
Y	0.00
X	15.00

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