Carrying out a usability test is a demanding process per se. Mobile tests raise this claim because they are subject to real usage conditions and therefore unforeseeable factors. On the one hand there are the technical factors like tools, software and laboratory equipment, but on the other hand there are the human beeings with their knowledge and decision-making. They are taking the selection of tools, methods and data, and they decide in every situation of the process of testing. Using a mobile eye-tracking test, the authors will explain where the sources for interpretation are and when misinterpretation become an error. Technology philosophical considerations on interpretation and hermeneutics have to support the recognition of the potential of interpretation. As a result, misinterpretation can be minimized.