HP 42S - Manual (Page 5)

So algebraic calculators are ambiguous because the many ways they work. RPN calculators are
more standard and so less ambiguous.
The main key to understand how to use RPN in more complex calculus is to realize that in RPN we
make calculations from “inside” to “outside” instead of from left to right.
Example:
8 x ln[5+sin(40)] in RPN is doing by
40 sin 5 + ln 8 x
In RPN we can make any calculation we do in algebraic devices and this is not only more elegant
but also more effective since there are less ambiguity's and we use less key strokes.
For example, my HP-33S, which is both algebraic and RPN, is always in RPN mode. (Just to insert
equations I think algebraic mode is better)
For more information on RPN, please see http://www.hpmuseum.org/rpn.htm
2.2 Turn ON/OFF
To turn your HP-42 on press ON. The ON key is the same EXIT key.
To turn your HP-42S off press ▀ OFF. OFF is in the same key of EXIT and ON, and by ▀ OFF we
mean you have to press the orange key before press the EXIT key which have OFF in orange above.
The orange ▀ key is what in some other calculators is called “second function”. When you press this
all keys turn in what is written in orange above it.
Actually ▀ OFF is a redundancy since OFF can be only accessed by pressing ▀ first. But (as in HP-
42S official manual) we will do this just to remember when we have to press ▀ or not. If you press
this key a second time all keys go back to the normal function.
2.3 Setting the display contrast
HP-42S, as most HP calculators, can set the display contrast by pressing at the same time ON and +
or -.
2.4 Training RPN using HP-42S
Now that you have your 42S on try to do the following calculations:
1) 6x(4+3).
Answer
4 ENTER 3 + 6 x
2) 2+{2x[2+(2/2)]}
Answer
2 ENTER 2 / 2 + 2 x 2 +