Clicking the mode button brings up the Options dialog which allows you to change the number base of the calculator or select special features, and to customize the appearance and behavior of the calculator. The mode dialog can also be invoked by right-clicking while the pointer is on the calculator body, or selecting Options from either the system menu or the menu/command bar (if activated).
Changing number mode changes the calculator display, but any data stored in the calculator is retained. Therefore you can convert between different number systems by entering data and then selecting the new number base. However, only the decimal system has a decimal point, the other number bases work for integers only. Also note that a number in one system will require a larger number of digits in a lower number base, which may cause an overflow. This is especially likely when converting to binary.
When converting between different number modes it is sometimes inconvenient to keep going to the Mode dialog. For quick Number Mode changes, use the accelerator or shortcut keys. These are all obtained by holding down Shift and Alt on the keyboard and typing the appropriate letter, i.e. D for Decimal, H for Hexadecimal, T for Time, etc. See the listing of keyboard accelerators.
Beyond base 16 it is not practical to provide buttons for letters, and the computer keyboard must be used. The convention is for the upper case letter to be used (i.e. shifted letter).
An interesting example is base 36, where all the decimal digits and all the letters of the alphabet are available. In this case, words can be encoded and made the subject of computation. This gives interesting possibilities for word games and simple ciphers.
Example:
GADGET - 3ZS45L = CALC98
Convert to Decimal:
743385932
Scientific calculators use algebraic precedence where multiplication and division take priority over addition and subtraction, regardless of the order in which the expression is presented. In this case "1 + 2 * 3" evaluates to 7, because "2*3" is evaluated first, and the result added to 1. This is the default precedence for Calc98.
The single level of built-in algebraic precedence may not be sufficient for more complex expressions, and the solution is to use parentheses.
Users of RPN (Reverse Polish Notation) calculators are able to perform complex calculations without parentheses because each value can be pushed onto a "stack" and the operators applied in order. This elegent method was available in early Hewlett-Packard scientific models before calculators with parentheses became available. Many of the users of these calculators prefer to continue using RPN, so this has been added as a third precedence option.
In RPN mode some of the button legends and behaviour change. In particular, the = button is labelled Enter and is used to enter or push a value onto the stack. The Min and MR buttons become STO and RCL respectively. There are no parenthesis buttons, but CLx and REG buttons are provided.