A method, apparatus, computer program, system and device for measuring oscillatory motion comprising: receiving a plurality of signals related to a plurality of measurements of a direction of a vector parameter (at-1, at); determining a predominant measured direction of the vector parameter (āt) based on the plurality of measurements of the direction of the vector parameter; determining an angle of rotation (φt) between: a measured direction of the vector parameter (at) of one of the plurality of measurements of the direction of the vector parameter, and the predominant measured direction of the vector parameter (āt).