You can create your own global variables, which are available for all solids in a model. Typically, you can give them names that simplify later identification where editing is required, or where you may want to use them on other solids. To avoid confusion with local variables, names for global variables must begin with an alpha character. Names for local variables always begin with the underscore character.

Global variables can be either driving or driven.

• Driving variable — like a constant in an equation. Can be changed only by manual editing.
• Driven variables — derived from the solution of an equation and cannot be edited manually. Changes to these occur, automatically, when a value (of a driving variable) in the equation is modified.

Consider, for example, a simple slab that always has its width as 0.5 times its length, and its height as 0.75 times its width. You could create a driving variable for its length, and driven variables for its width and height. In the case where the length is 5 units, then the global variables could be created as follows:

Driving variable — Length=5

Driven variables — Width=0.5*Length and Height=0.75*Width

In this case, the variables would have to be created in the order Length, Width, and Height, as each includes a reference to the previously defined variable. You cannot create an equation that references a nonexistent variable. With the above variables applied to the dimensions of the slab, only the value of Length is readily editable, but this would cause changes to the Width and Height of the slab, as per the driven variables.