HP 35s Instruction Manual page 2

hp calculators
HP 35s Using RPN Mode
Calculation modes
The HP 35s allows calculations to be made in "RPN" mode, in "algebraic" mode, or in "Equation" mode. Algebraic and
Equation modes and programs are described in other training aids.
RPN mode is the traditional way most HP calculators work. To add 1 and 2, keys are pressed in the order
1Ï2Ù. This mode is very suitable for calculations where the user is working towards a solution, without
having a particular formula to work on.
Note: When doing the examples press 95 to set RPN mode, or 94 to clear RPN mode and set algebraic
mode. The selected mode is shown at the top of the calculator screen.
Functions of a single number in RPN
In RPN mode, to square a number, the number is typed, then the º= key is pressed. If a second number is to be
squared, the steps are repeated.
A simple example in RPN
Example 1: A gardener wants to plant a triangular piece of ground and to put protective edges around the plot. The plot
will have a right angle and the two shorter edges will be 1.2m long and 0.5m long. How long will the third
edge be?
Solution: The length can be calculated using Pythagoras' formula. From a² + b² = c² the third side is:
c = √(a² + b²)
To calculate this, it is first necessary to square the numbers 1.2 and 0.5. On a calculator, the square of a
number is a function of a single number. It does not involve adding or multiplying two numbers.
To square 1.2 and 0.5, it is enough to type:
1Ë2º=Ë5º=
Answer: The second result, 0.25, is on the lower line of the calculator screen, called the X register. The previous
result, 1.2 squared, is on the upper line, called the Y register. Registers are places where numbers are held
in the calculator; X and Y are the first two registers in the RPN stack. The stack is the most important tool
in RPN calculations. Its use is shown later in this example.
Other functions of one number, for example sine, log or square root, work the same way. The number is
typed and shows up in the lower line, in the X register. Then the function key, for example k or ? is
pressed to give the answer. The square and square root keys are labeled with an "x" as a reminder that
they work on the number in the X register.
hp calculators - 2 -
Figure 1
HP 35s Using RPN Mode - Version 1.0