Im measuring the Cv of a valve using an inline flow meter upstream of the valve. My question is when you are measuring the flow, ALL of the water inside the pipe is moving at the same flow rate no matter where you are taking the measurement in regards to the position of the valve. There might be a small difference in flow rate initially when closing the valve if the flow meter is far upstream of the valve, but the difference is negligible, specially at a line pressure around 30psi. Is this thinking correct. Assuming that the water is laminar and not compressible flow rate readings will be identical no matter where you are measuring it? With a much more dense fluid like oil would it would make more of a difference right?