HP 33s - Manual (Page 47)

RPN: The Automatic Memory Stack 2–7
„ During program entry, b deletes the currently–displayed program line and
‡ cancels program entry.
„ During digit entry, b backspaces over the displayed number.
„ If the display shows a labeled number (such as /)
), pressing ‡
or b cancels that display and shows the X–register.
„ When viewing an equation, b displays the cursor at the end the equation
to allow for editing.
„ During equation entry, b backspaces over the displayed equation, one
function at a time.
For example, if you intended to enter 1 and 3 but mistakenly entered 1 and 2, this
is what you should do to correct your error:
T
Z
Y 1
1
1 1
X 1 1 2 0 3
1 2 3 4 5
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.