Patent ID: 8416102

Claim:
An activity monitoring system adapted to eliminate passive movement components caused by external forces from readout data produced by at least a first and a second motion sensor when attached to a subject during movement, the readout data including gravitational components, movement components caused by active movement of the subject or subject parts, and the passive movement components, the system comprising: a processor adapted to: estimate first and second gravitational components produced by the at least a first and a second motion sensors, determine a rotation matrix based on the first and second estimated gravitational components, the rotation matrix denoting rotation required for the first motion sensor to get aligned with the second motion sensor in orientation, multiply the readout data produced by the first motion sensor with the rotation matrix when rotating the first motion sensor towards the second motion sensor to produce a multiplied result, and subtract the multiplied result from the readout data produced by the second motion sensor when rotating the first motion sensor towards the second motion sensor.