Choose the Tools tab→Assistants group→Relationship Assistant command 
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Drag a fence around the profile elements you want to evaluate, and then click the Accept (check mark) button on the command bar.
On the command bar, click the Show Variability button.
Tip:
The Relationships Needed box on the command bar displays the number of relationships needed to fully constrain the profile. There is also graphical feedback which indicates how the profile can change.
If you select elements that cannot change as well as elements that can change, then Show Variability will indicate that no elements can change, and the number of relationships needed will be 0.