When editing numerical values of a feature, you can assign dimension in the form of algebraic equations. These equations can consist of numbers only (i.e. 5+6*3) or they can relate to other parameters.
Click the button in the Dimension
Dialog to create equations with parametric dependency. Simply click
on other dimensions to enter their ID's into your equation, and enter
the desired mathematical operation.
Allowable mathematical operations:
Important: If you enter an equation for a parameter, such as extrude length, when you return to the Feature Guide to edit the feature again, this parameter will be grayed out. This is to prevent you from entering a number and overriding the equation.
Example
Double-click on both of the features below to display their parametric values. The values displayed include the extrude lengths and dimensions of the sketches.
The width of the green object (now 42) should be dependent on the distance
from the cylinder center to the back of the box (now 21). Click the 42
dimension to open the Dimension Dialog,
and click the icon.
Now click the 21 dimension to enter its ID (L6) into the equation field.
This width value needs to always be double the L6 value. Complete the equation as L6*2.
To add another equation, click on the dimension for the diameter of the cylinder. Click the 42 value (whose ID is L2), and enter the equation shown below. Now whatever the width of the green object is, the diameter will always be 7 less.
To demonstrate the parametric dependency, change the 21 value to 27.
Click the 
icon to update the features.
The width of the green object is now 54 (=27*2) and the cylinder diameter is 47 (=54-7). If you open the Dimension Dialog for the width, you will see the equation you entered, rather than the numerical value. The L6 dimension used in the equation (27) is highlighted so that you can immediately see what values were used.
