The displayed fields (in this case base point X, base point Y, Width, Height) of the Change parameter window conform to the selected feature. In this window, you can assign equations and variables as well as concrete values.

Use the connected context menu (right-click into the respective field), in order to parametrize the respective sizes. Thus, variables, with the help of the menu points functions, operators, logic and Brackets can be connected to one another. Variables, functions, etc., are moved into the parameter field with a simple mouse-click and there attached to existing parameters.