A method and apparatus for measuring a resultant flow delivered by a pump coupled to an over pressure valve, the method comprising the steps of: measuring, using a first flow meter, feed flow to the pump; measuring, using a second flow meter, return flow from the over pressure valve; and calculating resultant flow, at least in part, by subtracting measured return flow from measured feed flow. A pump power modification module can further modifying the pump output pressure to enable pressure profiling.