HP 30b Professional manual

by an operation key. Pressing the Ikey is optional after entering a number, if the next key pressed is an operation. Each time you press an oper- ation or function key in RPN, the answer is calculated immediately and dis- played. For example, suppose you wanted to add two numbers in RPN, 1 and 2. Press 1I2+. The result, 3.00, is calculated and dis- played immediately.

There are four special registers used for storing numbers during calculations, 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. Most often, the number in the display is the number in the X-register. Primarily, the num- bers 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.

The Ikey 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 num- bers without reentering them. For more complex problems requiring two or more operations, you do not need to enter parentheses to set operational pri- ority. 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 inner- most parentheses and work your way out.

For example, in RPN mode calculate (3 + 4) ⋅ (5 + 6) . Although this is a simple example, you can use the principles introduced here when working with more complex problems.

12 Getting Started