HP 12C#ABA - 12C Financial Calculator Quick Start Manual page 12

The result, 3.00, is calculated and displayed immediately.
There are four special registers used for storing numbers during calcula-
tions, which are stacked on top of one another. Called "the stack," these
registers are designated X,Y, Z, and T. X is on the bottom, and T is on
the top. Unless the calculator is in Program mode, the number in the dis-
play is the number in the X-register. Primarily, the numbers in the X- and
Y-registers are the numbers used in calculations. The Z and T registers
are used for the automatic retention of intermediate results during chain
calculations.
R
The key separates numbers in the vertical stack and positions them
in the X- and Y-registers, and, in addition to displaying intermediate
results, this vertical arrangement of the stack allows you to copy and
rearrange numbers without reentering them. For more complex prob-
lems requiring two or more operations, you do not need to enter paren-
theses to set operational priority. Key in numbers and operations inside
the parentheses first, followed by those outside of the parentheses. If a
problem has more than one set of parentheses, start by working with the
operations and numbers in the innermost parentheses and work out.
( ) ( )
+ × +
3 4 5 6
For example, in RPN mode calculate . See
Table 1-2. Although this is a simple example, you can use the principles
introduced here when working with more complex problems.
8 Getting Started