Appendix A: RPN and the Stack 173
The diagram on page 167 illustrates how the automatic stack lift and stack drop
make chain calculations quick and error-free.
Virtually every chain calculation you are likely to encounter can be done using
only the four stack registers. However, to avoid having to store an intermediate
result in a storage register, you should begin every chain calculation at the inner-
most number or pair of parentheses and then work outward – just as you would if
you were doing the calculation manually (that is, using pencil and paper). For
example, consider the calculation of
3 [4 + 5 (6 + 7)]
If this calculation were done from left to right – as were the (simpler) examples
under Chain Calculations on pages page 21 and page 22 – you would have to
enter five numbers into the calculator before doing the first operation possible (6
+ 7). But since the stack holds only four numbers, this calculation cannot be
done left-to-right. However, it can easily be done if you begin with the calcula-
tion in the innermost pair of parentheses – again, (6 + 7).
Arithmetic Calculations with Constants
Because the number in the T-register remains there when the stack drops, this
number can be used as a constant in arithmetic operations. To place the constant
into the T-register, key it into the display (that is, into the X-register), then press
\ three times. This also places the constant in the Y- and Z-registers. Each
time an arithmetic operation is then performed – using the constant in the Y-reg-
ister and a number keyed into the displayed X-register – the constant will be
“dropped” back into the Y-register.
Example: The annual sales of solar engineering hardware your firm – currently
$84,000 – are projected to double each year for the next 3 years. Calculate the
annual sales for each of those years.
Keystrokes (RPN mode) Display
6\7+
13.00
Intermediate result of (6+7).
5§
65.00
Intermediate result of 5 (6+7).
4+
69.00
Intermediate result of [4 + 5(6 + 7)].
3§
207.00
Final result: 3 [4 + 5 (6 + 7)].
