There is an option to enter the Force and Area and have the Load automatically calculated. When this checkbox is selected, the Load textbox will be replaced by textboxes for Force and Area. These values will be used to calculate the load, and this calculated value will be used in the graphs and other calculations.
There is no limit for the entered force or area, but the calculated load needs to be within the operating limits of the design tool (0.004-0.2 N/mm2 / 0.59 - 29 psi).