To Create an Aligned Dimensional Constraint in the Content Editor (AutoCAD Mechanical Toolset)

In the Authoring Palettes window, in the Dimensional tab, click Aligned.
Select the two constraint points on the object.
Specify the dimension line location.
In the dimension text, specify a name for the dimensional constraint, to the left of the "=" sign.
Note: The dimension text of the form “name=value
Enter a value or specify an expression to the right of the "=" sign.
Note: If you specify an expression, it is local to the view you are editing. To make it valid across all views, add the dimension to the Family Table as a calculated column and specify the expression in the column properties.
Press Enter.