HP -28S Quick Reference page 5

COMMAND can be used to retrieve this stored command line for editing.
UNDO ENTER (or any other command that involves execution of ENTER) stores a
copy of the current stack before it executes provided MODE UNDO has
been activated (see MODE Menu).
UNDO recalls the previousely stored stack layout.
Note that this feature potentially requires a lot of memory!
LAST When a command takes arguments from the stack those arguments will be
saved provided MODE LAST has been specified (see MODE Menu).
LAST retrieves these saved arguments and pushes them back onto the
stack. Note that the number of saved stack arguments depends on the
command.
If MODE LAST is active and a command produces an error then the stack is
automatically restored. If MODE LAST is not active these arguments are
lost.
1/x Reciprocal of numbers or matrices.
Displayed in equations and programs using the INV() function notation.
STO Stores the object in stack level 2 in the variable who's quoted name is
given in stack level 1. Ie. 5 'A' STO stores 5 in variable A and drops both
objects from the stack. See STORE Menu.
RCL Recall variable and push it onto the stack. This does not evaluate the
contents of the variable or execute a program. The quoted variable name
is replaced by the recalled object. See STORE Menu.
PURGE Delete variable or program who's name is given in stack level 1. This
command can operate on lists of names! To erase all variables of the
current directory use MEMORY VARS PURGE
Warning: VARS also returns subdirectory names so in the above example
all subdirectories will be returned as well!!
See STORE Menu.
∫
Numeric or symbolic integration. See Integration.
d/dx Symbolic differentiation. See Differentiation.
^ Exponential function. Ie. –2 3 ^ returns –8 in stack level 1.
Accepts real and complex numbers.
EVAL Evaluate quoted name or program in stack level 1. See Evaluation Rules.
→NUM Same as EVAL but also converts a symbolic name into a number.
Ie. 3 π * results in '3*π' and →NUM converts this into 9.424...
CONT Continue an interrupted program. See Programs.
% Percentage.
Note that different from other HP calculators this does drop the stack.
%CH Percentual difference from contents in stack level 2 to contents in stack
level 1.
√X Square root. Displayed in equations and programs using the square root
symbol "√".
ON Turns calculator on, clears errors displays, aborts command line editing,
interrupts programs. ON never discards data from the stack.
OFF Turns calculator off.
It automatically turns itself off after a few minutes of inactivity.
CLEAR Clear the stack. See STACK Menu.
CONVERT Convert between different units. See UNITS menu.
HP-28S
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