  Two accelerometers are used to measure the motion of the golf club. The
accelerometers are mounted in the shaft of the golf club. Each measures the
acceleration along the axis of the shaft of the golf club. Interpreting the
measurement with the context of the double pendulum model of the golf swing, it
is useful to resolve the resulting signals into differential and common mode
components. The differential mode is a measure of the rotational kinetic energy
of the golf club, and this can be used to understand the tempo, rhythm, and
timing of the golf swing. The common mode measurement is related to the motion
of the hands. It is shown that both components can be used to recover the
motion of the swing within the context of the double pendulum model of the golf
swing.
