Abstract: A method is disclosed calibrating a volumetric fluid flow sensor having a pole magnet armature in which a direction of reciprocation of the armature is co-linear with a magnetic axis thereof and in which there is provide a magnetic field sensor for sensing the position and strength of the magnetic axis of the magnetic armature. A path of fluid flow is defined which includes an inlet channel for contaning the reciprocation of the magnetic armature and having an outlet channel radially oriented relative to the input channel and in fluid communication with the inlet channel. A calibration magnet, located co-axially with the armature magnet provides a repulsive force to the armature magnet which, in co-action with the fluid force of the measured volumetric fluid flow provided an adjustable point of equilibrium of the armature and thereby an adjustable actuation point thereof.