a flow impedance device is provided for an obstruction flowmeter for determining the flow rate of a compressible or incompressible fluid in a conduit . the flowmeter has means for measuring the temperature and pressure of the fluid as well as the pressure differential across the flow impedance device , and further means for computing a flow rate from the measured pressures . the flow impedance device includes a plate having a plurality of elongated openings arranged in a predetermined pattern . the plate is installed generally transversely in the conduit to force the fluid to flow through the plurality of elongated openings .