Once we have the hand's positions in space, we can use these spatial coordinates in an absolute, physical frame of reference (that of the room, for example), or in a relative, perceptual frame of reference (in relation to the coordinates of the torso or head, for example). In the latter case, we are more concerned with the construction of an instrument attached to its user than to the room. The user can move around in space while playing the instrument, without the mapping between gesture and sound effect changing.