2 Basic Operations
2.1 RPN
The HP-42S, like most old HP calculators, is a RPN calculator. RPN comes from “Reverse Polish
Notation”. In RPN we first enter data and then we enter the mathematical operations.
Example: To make a simple operation like 2+2 in a normal algebraic calculator we do “2 + 2 =”
which give to us 4. To make this same calculation using a RPN calculator we do “2 ENTER 2 +”
As we can see in RPN mode we first enter the data pressing the ENTER key after every data (except
for the last in HP's RPN) and then we enter the operations.
Let’s now consider the following calculation
4 + (2 × 79)
In a RPN calculator we do
2 ENTER 79 × 4 +
But how could one do this in an algebraic calculator? If the calculator has “(“ and “)” keys we enter
4 + ( 2 × 79 ) =
But if there are no parenthesis keys we might do this in a good calculator by doing
4 + 2 × 79 =
By a “good” calculator we mean a calculator which knows that “×” and “/” have precedence over “+”
and “–“. In a bad algebraic calculator which does not know this we have to do
2 × 79 =
and
+ 4 =
Or
2 × 79 + 4 =
What about to calculate sin(33°)? In a RPN calculator we enter
33 sin
or if you prefer
33 ENTER sin
(in this case we don't need to press enter key)
But in an algebraic calculator we have two ways. In the classic old models it is like RPN and we do
33 sin
but in some modern models (which typically allow you to edit entered data using cursors) we do
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