A system for determining an orientation of a first device relative to a user includes a first device including a first orientation measuring unit configured to measure an orientation of the first device relative to the earth, a second device configured to be worn by the user on a body part. The second device includes a second orientation measuring unit configured to measure an orientation of the second device relative to the earth. The system also has a processor configured to calculate an orientation of the first device relative to the second device by comparing the measured orientation of the first device relative to the earth with the measured orientation of the second device relative to the earth.