Tab: Pressing the tab key enters information and moves you to the next Calculator box. The tab key is the only way to move about the Calculator boxes in addition to the mouse.
F6: Pressing the F6 key on a Calculator box, recalculates the contents of that box. Left Clicking on the prompt message in front of that Calculator box also recalculates the contents of that Calculator box.
Enter: The Enter key purposely does not function inside the Calculator.
Mouse: The mouse, via left clicking, is the only way to enter or leave the Calculator.
Automatic Recalculation: You must retype information in all of the first three Calculator boxes in order for the fourth box (Payment:) to be automatically calculated. Even if a number is in the box that you want, you must still type over it in order for the calculator to recognize the change. Also, as long as any three of the first four boxes are changed the remaining box will be calculated.