HP 35s Scientific Calculator - Manual (Page 54)

2-8 RPN: The Automatic Memory Stack
1. Lifts the stack
2. Lifts the stack and replicates the X–register.
3. Overwrites the X–register.
4. Clears x by overwriting it with zero.
5. Overwrites x (replaces the zero.)
The LAST X Register
The LAST X register is a companion to the stack: it holds the number that was in the
X–register before the last numeric function was executed. (A numeric function is an
operation that produces a result from another number or numbers, such as
 .)
Pressing   returns this value into the X–register.
This ability to retrieve the "last x" has two main uses:
1. Correcting errors.
2. Reusing a number in a calculation.
See appendix B for a comprehensive list of the functions that save x in the LAST X
register.
T
Z
Y
1 1 1 1
1 X
1

1
2
2
C
0
3
3
1 2 3 4 5