Apparatus is provided to measure the amplitude and frequency of dynamic force exerted by a rotating shaft on an adjacent non-rotating bearing. The apparatus includes two force probes operatively mounted on the bearing to sense force components in two perpendicular directions. A piezo-electric load cell in each force probe senses the frequency and a proportional amount of the amplitude of the force component in its direction, and converts such sensed frequency and amplitude into an electrical signal. The sensed amplitude in each direction is calibrated to actual amplitude. The calibrated signals from the two force probes are supplied to an oscilloscope to display a composite representation of such dynamic force in a plane including the two directions. In use, the apparatus performs a novel method of measuring such dynamic force.