Click on the smaller of the two calculator icons at the left to reveal a basic calculator to do simple computations. It should appear as shown below.
The keys and/or keyboard may be used to enter numbers and parenthesis on the display. The square root key (√) will return the square root of whatever is on the display. The % key will change your result to percent. The 1/x key will take the reciprical of the number shown. The equal key will compute whatever you have entered.
The (C) or clear key clears the calculator display. You must clear the display between calculations unless it is your intent to chain computations.
Note that you can drag and drop this calculator any place on the screen. If you no longer need it, you can close it by clicking on the 'X' in the upper right had corner.