An assembly installable in an air conditioning and/or heating system of a room including a body (7) having an inlet opening (7a), an outlet opening (7z) and a channel (70) providing fluid communication between the inlet and outlet openings (7a, 7z). An orifice in the body (7) and shaped such that when a flow runs through the channel (70) between the inlet opening (7a) and the outlet opening (7z), a pressure difference is generated between the first region (7p) and the second region (7s) within the body (7), the first region (7p) being located upstream of the orifice, the second region (7s) downstream of the orifice. The assembly includes a meter (1) for detecting the pressure difference and a variator of at least one geometric feature of the orifice, the variator being able to arrange the orifice in different configurations, each corresponding to a respective geometric feature of the orifice.