According to the present invention a flow meter is provided for measuring a fluid, comprising a measuring tube with a measuring piston movably arranged in said measuring tube, and elements for changing the direction of movement of the measuring piston in said measuring tube, wherein said measuring piston, when measuring, is designed to be moved in said measuring tube under the influence of said fluid. Sensor elements detect movement of the piston and the direction of movement in said measuring tube, and sensor elements detect when the piston is situated in at least one of its reversing areas before the measuring piston has reached the extreme point of the reversing area, so as to afford a substantially continuous flow detection for said fluid.