In the DFG program:
“Analysis, modelling and calculation of flow mixers with and without chemical reactions (SPP 1441)”
there are used different mixing machines (reactors), different objectives and different dimensions. All research programs, however, have in common, that they have to evaluate the mixture concerning its “quality”. There are totally different measured variables, measuring methods and methods of taking samples employed. Together with different “mixedness definitions”, it is difficult, if not impossible, to compare the results with regard to their “mixing efficiency”. The publication presented tries to express the fundamental requirements and dependencies of the definition “mixedness” to avoid these problems.