Abstract: A self-calibrating apparatus and a self-calibrating method for measuring the pressure distribution generated by a three-dimensional object, is described which includes a plurality of first non-linear force sensors arranged in an array; and a second force sensing device (3) having a linear or linearisable output for measuring the total force applied to the first force sensors. The first sensors are dynamically calibrated based on the results of the comparison. The three-dimensional object may be a human foot and the apparatus and method amy be sued for fitting shoes or for determining irregularities or ailments of the human foot or leg.