HP 33s Scientific manual X and Y-Registers are in the Display, Clearing the X-Register

T0.0000 "Oldest" number

Z0.0000

Y

X

0.0000

0.0000

Displayed

Displayed

The most "recent" number is in the X–register: this is the number you see in the second line of the display.

In programming, the stack is used to perform calculations, to temporarily store intermediate results, to pass stored data (variables) among programs and subroutines, to accept input, and to deliver output.

The X and Y–Registers are in the Display

The X and Y–Registers are what you see except when a menu, a message, or a program line is being displayed. You might have noticed that several function names include an x or y.

This is no coincidence: these letters refer to the X– and Y–registers. For example,

{raises ten to the power of the number in the X–register.

Clearing the X–Register

Pressing {c{º} always clears the X–register to zero; it is also used to program this instruction. The ‡key, in contrast, is context–sensitive. It either clears or cancels the current display, depending on the situation: it acts like { c{º} only when the X–register is displayed. balso acts like {c {º} when the X–register is displayed and digit entry is terminated (no cursor present). It cancels other displays: menus, labeled numbers, messages, equation entry, and program entry.

2–2RPN: The Automatic Memory Stack