https://forums.autodesk.com/t5/inventor-forum/dimensions-needed/m-p/5743542#M366860 In logic, there are a set of axioms, and from these axioms one derives a set of theorems and lemmas. I agree that your answer is correct; what is missing is a well-defined set of axioms. Instead, I am forced to infer the axioms, and therefore I lack critical facts necessary for correct inference. I treated construction lines as abstract line segments not requiring a length if their position were constrained. But then, I should have been able to learn this when I looked up the error in the documentation.<BR />joe Mon, 27 Jul 2015 18:51:18 GMT Anonymous 2015-07-27T18:51:18Z