Fundamentals > Relations and Parameters > Relations > Basic Relations Information > Rules for Using Relations
  
Rules for Using Relations
Consider the following rules:
If you try to assign a relation outside the section to a parameter that is already driven by a section relation, you get an error message when the system regenerates the model. The same applies if you try to assign a relation in a section to a parameter that is already driven by a relation outside the section. Remove one of the relations and regenerate model.
If an assembly tries to assign a value to a dimension variable that is already driven by a part or subassembly relation, you get an error message. Remove one of the relations and regenerate the model.
Modifying the units of a model can invalidate your relations, as they are not scaled along with the model.
The relations are evaluated from top to bottom. After executing the relations, the final values of the parameters are locked. However, if a parameter value is based on a condition, the parameter is locked only if the condition remains true after executing all the relations.
 
* In some cases, relations defined at different levels may conflict. Check the validity of relations by clicking and make sure your relations fulfill your design intent.