The X And Y-Registers Are In The Display; Clearing The X-Register; Reviewing The Stack - HP 35s User Manual

The X and Y–Registers are in the Display
The X and Y–Registers are what you see except when a menu, a message, an
equation line ,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
program this instruction. The
or cancels the current display, depending on the situation: it acts like
 1
() only when the X–register is displayed.
 
() when the X–register is displayed and digit entry is terminated
(no cursor present).

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 the numbers
as they roll through the x- and y-registers.
Suppose the stack is filled with 1, 2, 3, 4. (press

all the way around and back to where they started:
T
1
Z
2
Y
3
X
4

() always clears the X–register to zero; it is also used to

key, in contrast, is context–sensitive. It either clears
4
1
2
3
RPN: The Automatic Memory Stack

) Pressing four times rolls the numbers
3
4
1
2

also acts like
2 1
3 2
4
3
1 4
2-3