Gcalctool is the default GNOME desktop calculator.

Gcalctool has Basic, Financial and Scientific modes. Internally it uses multiple precision arithmetic to produce results to a high degree of accuracy.

Calctool is a desktop calculator. It has been designed to be used with either the mouse or the keyboard. It is visually similar to a lot of hand-held calculators. There are financial, logical and scientific modes. Similar operations are color coded. Some of the calculator keys have menu marks. This indicates that there is a menu associated with that key.

One of the most important things to remember about calctool is that calculations are performed from left to right, with no arithmetic precedence. If you need arithmetic precedence, then you should use parentheses.

Internal arithmetic is now done with multi-precision floating point numbers. Accuracy can be adjusted from zero to nine numeric places in fixed notation, but numbers can be displayed in engineering and scientific notation as well. The calculator reverts to scientific notation when the number is larger than the display would allow in fixed notation. The base of operation can be changed between binary, octal, decimal and hexadecimal. Numbers are initially displayed in fixed notation to two numeric places, in the decimal base.

There are ten memory registers. Numbers can be stored or retrieved in these locations, and arithmetic can be performed upon register contents.

The display windows contains the current numerical value plus the current base and trigonometric type. There are also indicators which show if the hyperbolic and inverse function switches are set, and which numerical mode is currently in operation. If an operation needing more than one numerical input is partially complete, the operation is also displayed in this window as a reminder.