In general, dynamic modelling of a physical system renders an under determinated DAE system. One has to choose some inputs to get a fully determinated system. If the resulting system has index one, the chosen inputs form a "low index assignment". However this assignment need not be unique. A consistent match of interconnected index one models-that consequently is not unique either-is desired to be found for model building and model re-use. This is a difficult task. Therefore, a structural detection method for all low index assignments using only "structural" information is presented. Once found they will help the modeller to look for a low index representation. An application is given to demonstrate the use of this algorithm.