Arrangement of the regulation section allows for the verification of the measuring gauges, at which, after the presetting of the required overflows, actuated individual tests immediately one after the other, while presetting of the regulation valve is not necessary (each of the three tested overflows is directed to a different branch). In case that values of two consecutive overflows are covered by the size of the flowmeter P3, water is supplied to the flowmeter directed by the couple of parallel branches embedded with the closing valves K3.l, K3.2 and the regulation valves RV3.1, RV3.2.