In order to define the performance of a position sensor, it is necessary to have strict definitions for the characteristics of interest.At present, terms such as accuracy, precision, nonlinearity and resolution are defined loosely and often vary between manufacturers and researchers. The lack of a universal standard makes it difficult to predict the performance of a particular sensor from a set of specifications. Furthermore, specifications may not be in a form that permits the prediction of closed-loop performance. This article provides concise definitions for the linearity, drift,bandwidth and resolution of position sensors. The measurement errors resulting from each source are then quantified and bounded to permit a straightforward comparison between sensors. An emphasis is placed on specifications that allow the prediction of closed-loop performance as a function of the controller bandwidth