T Z Y X; Figure 2 - HP 20b Instruction Manual

hp calculators
HP 20b Using the RPN stack to solve problems efficiently
The benefits of understanding RPN stack operations
RPN stands for Reverse Polish Notation and is one of two operating modes available on the HP 20b. Mastering RPN
leads to an enhanced performance when using the calculator. The first step to master RPN usage is to know all of its
available resources.
To put the HP 20b into RPN mode, press :u, then press < five times. The display should show either Chain,
Algebraic or RPN. If it does not show RPN and you wish to put the HP 20b into RPN mode, press I until the
display shows RPN (which would only take one or two times). To exit this menu, press O.
When RPN mode is active, the RPN annunciator is visible in the display as shown in figure 2 below.
Understanding the HP 20b stack operation in RPN mode
When in normal, 'run' mode, every operation performed in the HP 20b uses the display contents or places results on it.
The display always shows the contents of the X-register. A register is a predefined place in the calculator memory that is
able to hold a formatted number with a twelve-digit mantissa and a three-digit exponent of ten. The X-register is one of
five registers that form the RPN stack, represented in Figure 1 with all contents cleared to zero.
Anytime a number is keyed in, the X-register is updated to hold this number. It is then available for use.
Example 1: What is the most common keystroke sequence to compute the reciprocal of 7.2? What registers in the
stack are used?
Solution: The most common keystroke sequence to compute the reciprocal of 7.2 is:
7.2:i
In this case, simply typing in the number and pressing the related key are enough to compute the resulting
value. There are other functions that use only the X-register contents, like :g or :r. These are
the 'one-number functions', and when they are pressed, the calculator proceeds with the following
operation sequence:
hp calculators
Stack registers
ANS
Figure 1
T
Z
Y
(normally shown in the display)
X
- 2 - HP 20b Using the RPN stack to solve problems efficiently - Version 1.0

Figure 2