It's not a new idea but it sure is new to AutoCAD. The same 2D sketch constraints that have been available in Autodesk Inventor are now in AutoCAD. I'll show you how to get your feet wet with parametric design.
Geometric constraints create relationships between lines, splines, and arcs that maintain the shape of your design. Instead of me trying to explain this, just take a look.
Check back for Part 2: Dimensional Constraints
Blogged by Josh Hunt, Yet another CAD Geek
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