The External Assessment Centre highlighted that the battery life of VibraTip has implications for the cost modelling. The Horsfield and Levy (2013) study was a technical assessment of 3 different activation patterns of VibraTip and the influence of these on battery life and the consistency of the stimulus. Results from a pattern designed to mimic use in clinical practice, showed that the amplitude reduced to 64% of its initial value after 3500 activations, but the frequency only reduced to 94%. The authors concluded that each VibraTip could test at least 100 patients. The External Assessment Centre considered that there is some uncertainty about the estimate of 100 patients because the duration of each activation in the study was 0.5 seconds instead of the 1 second duration recommended in the VibraTip Instruction for Use. The External Assessment Centre concluded that poor repeatability of the stimulus due to reductions in the amplitude over time is an important limitation to the clinical repeatability of the test, and the effect of these reductions in amplitude on diagnostic accuracy are unknown.