Laminar flowmeters fill a special need in flow measurement where the requirements might include low to extremely low flow rates, linear calibration and low noise, ability to measure high-viscosity liquids, or steady low flow repeatability and control accuracy. The basis of the device is the establishment of laminar flow between the pressure taps, and use of the well-known relationship between laminar flow rate through a tube of known cross-sectional area and the pressure drop across its known length. The flowmeter consists of the laminar flow element and a differential pressure-measuring instrument. The meter is sized properly for the flow in the passages to remain laminar, even at the highest rated flow. They produce a pressure difference, which is measured using an auxiliary instrument. The pressure drop across a well-designed laminar flowmeter is linearly proportional to the volume flow rate divided by the viscosity of the fluid flowing.