Abstract: There is described a portable wrist worn device for determining information about the movement of a human body when swimming. The device comprises a waterproof housing containing: an accelerometer operable to generate an acceleration signal; a processor operable to process the acceleration signal so as to generate one or more metrics relating to the movement of the human body; and a means for feedback of the one or more metrics to the user. The accelerometer may be operable to generate an acceleration signal along an axis parallel to the proximo-distal axis of the user's arm in use and/or the accelerometer may be operable to generate an acceleration signal along an axis parallel to the dorsal-palmar axis of the user's hand in use. The device may also be used in sports other than swimming.