1st Calculator is an expression calculator and unit converter which allows you to directly enter an expression to be evaluated. It is a handy and nice skinnable replacement for the standard Windows calculator with many additional features. 1st Calculator Main Features:

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Fully customizable interface with skins support

Can be called by pressing just one button

All arithmetic operations and over 20 functions

Editable lists of constants and unit conversions

Recalling previously calculated expressions

Five result formats with changeable precision

Automatic clipboard copy/paste

Minimizes to the system tray