Embodiments disclosed herein provide restrictive-flow flow measurement devices, valve improvements and signal control devices and processes that control the flow of liquids, including control processes for single-liquid calibration. In some embodiments, a fluid flow device can be calibrated using a single standard calibration fluid. The fluid flow of a first fluid through a flow meter is measured by calculating a first pressure difference between pressures sensed by two pressure sensors of the flow meter. The fluid flow of a second fluid through the flow meter is measured by calculating a second pressure difference between pressures sensed by the same two pressure sensors. A calibration coefficient is determined based upon the relationship between the flow rate, the fluid density and the calculated pressure difference for the first and second fluids. A relationship between the calibration coefficient and the kinematic viscosity of each fluid is then determined and stored.