The second reason is necessity of multiple data source acquisition. Testing in usability lab can be successfully executed using one camera for screen recording and
eventually second camera for user's face. In mobile environment, use of only one camera may be insufficient. There is no ideal place where to put the camera to record
device screen, another camera may be requested to record the environment. Nevertheless we can observe occurrence of events that are hard to explain, because they are not
correctly recorded due to complexity of events in mobile environment. We can face this issue by recording other data like behavior of tested application but that brings
another complexity to the process of usability data analysis. On the other hand, by increasing the number of data sources we can lower the possibility to misunderstand
situations that are potential usability problems. To effectively work with multiple data sources we need to synchronize them and present them in different way e.g.
by means of interactive visualization environment.