The expression calculation is performed by pressing the "=" button or clicking its symbol in the toolbar. The calculation at the moment is marked with a colored square box.
As it was mentioned above, the length (digits count) and value of the number have no limits. This means that you can use any digits in a number and any numbers in your calculations.
Example:
Each sub-expression can be calculated. This is achieved by selecting the necessary expression and pressing [Ctrl]-[=].
Example:
Take the previous expression, select the denominator, and press [Ctrl]-[=]. Result: