HP -28S Manual page 298

The HP-28S has no fixed size to its stack. As you enter new objects
onto the stack, new levels are dynamically created as they are needed.
When you remove objects from the stack, the stack shrinks, even to
the point where the stack is empty. Thus the HP-28S can generate a
Too
Fe~!
A .... gurnen t s
error that previous HP RPN calculators could
not.
The dynamic versus fixed stack implementation gives rise to the fol-
lowing specific differences between the HP-28S and fixed-stack
calculators:
Numbered levels. The indefinite size of the HP-28S stack makes the
X Y Z T stack level names inappropriate-instead, the levels are num-
bered. Thus level 1 is analogous to the X-register, 2 to Y, 3 to Z, and 4
to T. The key labels 1jx and x
2
were preserved on the HP-28S for the
sake of familiarity-they make the keys more visible than their actual
command names INV and SQ, respectively. However, the RPN fix-
ture X
< >
Y has been renamed SWAP on the HP-28S.
Stack Manipulation. The HP-28S requires a more general set of
stack manipulation commands than the fixed-stack calculators. Rt and
R~,
for example, are replaced by ROLL and ROLLO, respectively,
each of which require an additional argument to specify how many
stack levels to roll. The STACK menu contains several stack manipu-
lation commands that do not exist on the fixed-stack calculators.
No Automatic Replication of the T·register. On fixed-stack calcu-
lators, the contents of the T -register are duplicated into the Z-register
whenever the stack "drops" (that is, when a number is removed from
the stack). This provides a convenient means for constant multiplica-
tion-you can fill the stack with copies of a constant, then multiply it
by a series of numbers by entering each number, pressing
0,
then
1
CLx
1
after you have recorded each result. You can't do this on the
HP-28S-but it is easy to create a program of the form
« 12345
*
» 'MULT' STO
where 12345 represents a typical constant. Then all you have to do is
press
1
USER
I,
enter a number and press
MUL T ,
enter a new number
and press
MUL T
again, and so on, to perform constant multiplication.
You can leave successive results on the stack.
B: Notes for HP RPN Calculator Users 297