ReactOS Calc implements the standard arithmetic rules with the following operators:
Addition
Subtraction
Multiplication
Division
Remainder of a division
Those rules express the concept of priority.
Here there is a list of priorities implemented from the highest to the lowest:
Special functions which change directly the current value into a new one: trigonometrics, hyperbolics, exponentials and logarithms, reciprocal, base conversions, integer and fractional part detection and change of sign.
Power and root functions.
Multiplications, divisions, remainders.
Additions, subtractions.
Logical functions.
These rules may be overcome by using parentheses.
With 
and 
buttons, the user can isolate a mathematical expression to be evaluated separately. The number of parentheses into a single expression is virtually unlimited.
The number of currently-open parentheses is displayed in the left box underneath the base change option set.