The swim turn makes up a substantial portion of the total swim time in competition, and efficient turns can determine finishing positions in many competitions. Swim turns can be a neglected area of performance gain. This is largely due to the difficulty in extracting performance measures that might lead to improvement. An inertial sensor was used to assess the different phases of the swimming turn and the data were then compared to the synchronised video data. As a case study, two elite swimmers, a competitive pool swimmer and an elite Triathlete, were compared as a demonstration of the technology as a potential tool for routine use. The participants were asked to perform their typical tumble turn at two velocities. Timing of the rotation relative to the turn's push off was measured. The inertial sensor detected differences in rotation between the two swimmers tested. The sensor reported that push off occurred for the competitive swimmer before 90࡮d for the Triathlete after 90௦ rotation and was confirmed by video footage.