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File name: hp 12c_user's guide_English_HDPMBF12E44 Page: 170 of 209
Printered Date: 2005/7/29 Dimension: 14.8 cm x 21 cm
Appendix A
The Automatic Memory Stack
Four special re
g
isters in the hp 12c are used for storin
g
numbers durin
g
calculations. To understand how these
re
g
isters are used, they should be visualized as stacked on
top of each other.
(For this reason, they are
g
enerally referred to as the “stack re
g
isters” or
collectively as “the stack.”) The stack registers are designated X, Y, Z, and T.
Unless the calculator is in Program mode, the number shown in the display is the
number in the X-register (modified according to the current display format).
The number in the X-register — and, for two-number functions, the number in the
Y-register — are the number(s) used in calculations. The Z- and T-registers are used
primarily for the automatic retention of intermediate results during chain
calculations, as described in section 1.
Before we discuss the details of the stack operation, let’s take a quick look at how
the stack is used in a simple arithmetic calculation and in a chain calculation. For
each key pressed in the keystroke sequence, the diagram illustrating the
calculation shows, above the key, the numbers in each of the stack registers after
that key is pressed.
First, let’s consider the calculation of 5 – 2:
The diagram shows why we said in section 1 that the
\
key separates the
second number entered from the first number entered. Note also that this positions
the 5 in the Y-register above the 2 in the X-register — just like they would be
positioned if you wrote the calculation vertically on paper: