HP -28S Manual page 302

LASTX Versus LAST
The LASTX command on fixed-stack calculators returns the contents
of the LASTX (or L) register, which contains the last value used from
the X-register. This concept is generalized on the HP-28S to the LAST
command, which returns the last one, two, or three arguments taken
from the stack by a command (no command uses more than three
arguments). Thus 1 2
+
LASTX returns 3 and 2 to the stack on a
fixed-stack calculator, but 1 2
+
LAST returns 3,
1,
and 2 to the stack
on the HP-28S.
Although the HP-28S LAST is more flexible than its LASTX predeces-
sor, you should keep in mind that more HP-28S commands use
arguments from the stack than their fixed-stack calculator counter-
parts. This means that the LAST arguments are updated more
frequently, and even such commands as DROP or ROLL will replace
the LAST arguments.
Remember also that UNDO can replace the entire stack, which for
simple error recovery may be preferable to LAST.
B: Notes for HP RPN Calculator Users 301