The presence of one or more common elements in different layers often complicates or hampers the analysis of a multilayer thin film system. Some constraints or preconditions are usually required in order to reach a mathematical solution. For example, either the concentration(s) of the common element(s) in, or the thickness(es) of one of the relevant layers must be known.

An alternative approach is the use of more than one analyzing line for the element in question. Although this approach has long been proposed, there have been no detailed studies seen in literature. An attraction of using this approach is that it requires no prior knowledge of either the concentration or the thickness. The author has implemented this approach, and studied in detail its feasibility and pitfalls for practical applications.