A wrist worn pedometer includes a multiple axis inertial sensor. Signals from each axis of the multiple axis inertial sensor are received and are separately analyzed to determine which axis is producing a stable periodic signal, which is selected as the counting axis, i.e., the axis to be used for counting steps. Additionally, the pedometer determines whether the counting axis is registering arm movement or footsteps. The user's steps are counted based on the detected events, e.g., detected peaks or intervals between peaks, on the signal from the counting axis. One step per detected event is counted if the counting axis is registering footsteps and two steps per detected event are counted if the counting axis is registering arm movement. If the stability of the selected counting axis is lost, another axis is selected as the counting axis if it is producing a stable periodic signal.