This is a simple calculator that uses ONP notation. It supports basic operations such as addition, subtraction, multiplication, division as well as parentheses. To use it, simply enter the expression in the console and press enter. Formulas should be inputed using a standard human readable notation. Program then converts in into a ONP notation and calculates the result. The result will be displayed in the console, after a full process is shown, with each step of the evaluation process.