Most primary shock calibrations, or absolute shock calibrations, are currently performed using laser interferometry under the guideline of the international standard (ISO 16063-13, 2001). The laser interferometric method measures the displacement of a moving anvil with a shock accelerometer mounted on. To achieve high accuracy in the measurement of acceleration it requires a straight motion of the accelerometer with desired shock pulse duration and shape. Unfortunately, shock generators usually present high levels of unwanted motions, such as rotation, transverse motion, and pitch motion. The presence of unsymmetric forces on the anvil causes these motions. To reduce the effect of these motions, measurements may be performed at multiple incidence points equally spaced along the border of the accelerometer on the mounting surface or on the top surface of the accelerometer and the corresponding average is then estimated. Obviously, this method is very time consuming. Alternatively, supporting structures can be added to the anvil in such a way that few or no unsymmetric forces cause rotation and deviations from rectilinear motion. To obtain the best results, the supporting structure should be optimized for a specific type of accelerometer with its dummy mass if any. For this purpose, a real-time anvil motion monitoring system was developed at National Research Council Canada. This paper describes the detail of the system and presents the measurement results under different operating conditions. Static air bearing measurements were performed using the system to study the radial stiffness and pitch stiffness of the anvil. Dynamic air bearing measurements were also performed using the system to ensure that the resonance frequencies of the anvil are at least 10/T, where T is the pulse duration.