The X And Y-Registers Are In The Display; Clearing The X-Register; Reviewing The Stack - HP 33s Owner's Manual

The most "recent" number is in the X–register: this is the number you see in 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,
¹ !
raises ten to the power of the number in the X–register.
Clearing the X–Register
¹ ¡
Pressing
program this instruction. The
clears or cancels the current display, depending on the situation: it acts like
¡
{  } only when the X–register is displayed.
{  } 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.

Reviewing the stack

R (Roll Down)
<
The (roll down) key lets you review the entire contents of the stack by
"rolling" the contents downward, one register at a time. You can see each
number when it enters the X–register.
2–2
RPN: The Automatic Memory Stack
File name 33s-E-Manual-1008-Publication(1st).doc
Printed Date : 2003/10/8
T
0.0000
"Oldest" number
Z
0.0000
Y
Displayed
0.0000
X
0.0000
Displayed
{  } always clears the X–register to zero; it is also used to
Å
key, in contrast, is context–sensitive. It either
Size : 13.7 x 21.2 cm
~
also acts like
Page : 386
¹
¹ ¡