HP 113394 User Guide - Page 228

Appendix A RPN and the Stack In RPN mode, four special registers in the hp 12c platinum are used for storing numbers during calculations. To understand how these registers are used, they should be visualized as stacked on top of each other. (For this reason, they are generally referred to as the "stack registers" 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: 228 File name: hp 12c pt_user's guide_English_HDPMF123E27 Page: 228 of 275 Printed Date: 2005/8/1 Dimension: 14.8 cm x 21 cm