We found this comment of the Autodesk discussion boards. It may help answer your question.

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Reply From: Brian R. Iwaskewycz
Date: Mar/31/06 - 14:28 (CST) NEW!

Use the Auto Dimension tool. If it reports that zero constraints/dimensions are required, then your sketch is fully constrained.

Brian R. Iwaskewycz
CAD Systems Manager
Core Furnace Systems

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Thanks.
3DCADTips Support Desk