An apparatus for measuring a physiological parameter of a user is disclosed. The apparatus comprises at least one processor and at least one memory comprising a computer program code comprising program instructions of a first algorithm modelling acquisition of the physiological parameter from motion of a user's arm and program instructions of a second algorithm modelling acquisition of the physiological parameter from motion of the user's torso. The at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: acquire torso acceleration data representing motion of the torso of the user； process the torso acceleration data with the second algorithm； and acquire, from the acceleration data processed with the second algorithm, reference parameters for the first algorithm.
