Apparatus designed to measure the flow of a flowing fluid according to the electromagnetic measuring principle, with a measuring tube with at least two consecutive subsections (11, 11') in the flow direction of the fluid, wherein the subsections (11, 11') differ from one another in terms of the diameter and/or geometry of the cross-sectional area in such a way that, at a given flow, different flow velocities of the flowing fluid prevail in the at least two subsections, at least a magnet system (9, 9') with at least two coils for the generation of a magnetic field essentially perpendicular to the flow direction of the fluid, at least two pairs of measuring electrodes (8, 8') to measure the induced voltage, wherein at least one pair of measuring electrodes is arranged in a first subsection and a second pair of measuring electrodes is arranged in a second subsection, wherein each pair of measuring electrodes (8, 8') comprises a first and a second measuring electrode, wherein the measuring electrodes are opposed to one another in or on the measuring tube and the connecting line of the measuring electrodes is oriented perpendicular to the tube axis et perpendicular to the magnetic field, and an electronic unit designed for signal measurement and/or evaluation, and to feed the coils, wherein said electronic unit is designed in such a way that it determines, for each subsection (11, 11'), the flow velocity of the fluid and/or the flow rate from the induced voltage, it determines, for each subsection (11, 11'), a transition zone between laminar and turbulent flow, it checks, for each subsection, whether the transition zone between the laminar flow and the turbulent flow is present for a measurement, it selects, for the purpose of determining the flow, a subsection (11, 11') in which the prevailing flow profile is essentially situated outside the transition zone (12, 12') between the laminar flow and the turbulent flow. a measuring tube with at least two consecutive subsections (11, 11') in the flow direction of the fluid, wherein the subsections (11, 11') differ from one another in terms of the diameter and/or geometry of the cross-sectional area in such a way that, at a given flow, different flow velocities of the flowing fluid prevail in the at least two subsections, at least a magnet system (9, 9') with at least two coils for the generation of a magnetic field essentially perpendicular to the flow direction of the fluid, at least two pairs of measuring electrodes (8, 8') to measure the induced voltage, wherein at least one pair of measuring electrodes is arranged in a first subsection and a second pair of measuring electrodes is arranged in a second subsection, wherein each pair of measuring electrodes (8, 8') comprises a first and a second measuring electrode, wherein the measuring electrodes are opposed to one another in or on the measuring tube and the connecting line of the measuring electrodes is oriented perpendicular to the tube axis et perpendicular to the magnetic field, and an electronic unit designed for signal measurement and/or evaluation, and to feed the coils, wherein said electronic unit is designed in such a way that it determines, for each subsection (11, 11'), the flow velocity of the fluid and/or the flow rate from the induced voltage, it determines, for each subsection (11, 11'), a transition zone between laminar and turbulent flow, it checks, for each subsection, whether the transition zone between the laminar flow and the turbulent flow is present for a measurement, it selects, for the purpose of determining the flow, a subsection (11, 11') in which the prevailing flow profile is essentially situated outside the transition zone (12, 12') between the laminar flow and the turbulent flow.