A system including: a first sensor module having an inertial measurement unit and attached to a palm of a hand of a user; a second sensor module having an inertial measurement unit and attached to a first bone of a finger (e.g., a middle or proximal phalange bone) on the palm; and a computing device coupled to the first sensor module and the second sensor module to calculate, based on the orientation of the palm and the orientation of the first bone, orientations of the second bones of the finger (e.g., a distal or proximal phalange bone, a metacarpal bone of the thumb) that have no separately attached inertial measurement unit, according to a predetermined ratio of rotation from a reference orientation along a same axis of rotation.