The motion estimation unit comprises a first summation means for calculating match errors of a number of candidate motion vectors of a segment of a first image. The probabilistic analysis is based on finite element modeling, in which uncertainties in the modeled system are represented by changes in the nominal geometry of the model, referred to as \u201cperturbations\u201d. Embodiments comprise methods and apparatuses arranged to measure temperature based upon current leakage rates of different integrated circuit sensor elements. The method includes reading device information from a memory on the subsystem and determining whether the subsystem operates in a multi-source mode responsive to the device information.