In Mission 4 of the Apocalypse Trigger you use parametric constraints in AutoCAD 2013 to accurately and efficiently create the doors and windows for an elevation of a bell tower.

After creating a vertical line down the center of the tower, you begin applying geometric constraints to the doorway geometry. Using coincident, equal, symmetric, and other geometric constraints, you clean up what was originally a rough (sloppy) sketch to
ensure proper relationships between geometry. The AutoConstrain tool gives you a head start by applying many of the constraints automatically.

You’ll continue to apply geometric constraints to the windows in the upper floors and you’ll use the Infer Constraints tool to automatically apply relevant geometric constraints to newly created geometry.

After applying geometric constraints, you continue defining the shape of the geometry by applying dimensional constraints. You give meaningful names to the dimensional constraints and, where appropriate, you use the same name for multiple dimensions.

After applying dimensional constraints to all the door and window geometry in the bell tower, you change the constraint form of some of the dimensional constraints to annotational. Those annotational constraints not only drive the geometry but they can be displayed and plotted similar to traditional dimensions.

Finally, to experience the ultimate power of parametric constraints, you edit parametric dimension values in the Parameters Manager and watch as the drawing geometry dynamically updates while maintaining all the geometric and dimensional relationships that you applied.