HP 42S manual Basic Operations, Rpn

2 Basic Operations

2.1 RPN

HP-42S as most old HP calculators was 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 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.

Lets now consider the following calculation 4+(2x79).

In a RPN calculator we do 2 ENTER 79 x 4 +

But how one could do this in an algebraic calculator? If the calculator has the ( and ) sings it is just do

4 + ( 2 x 79 ) =

But if there are no () we do this in a good calculator by doing 4 + 2 x 79 =

By a good calculator we mean a calculator which knows that x and / are prior to + and -. In a bad algebraic calculator which does not know this we have to do

2 x 79 = and

4 + = or

2 x 79 + 4 =

What about calculate sin(33)? In a RPN calculator it is just do 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 sin 33 =