Glass calibration cylinders are installed in the suction line to the chemical metering pump. Two isolating valves are installed in the suction line. The top of the cylinder should be vented back to the storage tank or to drain. Fill the cylinder to the top mark then close the valve from the chemical tank. Switch on the chemical feed pump and draw down the chemical in the cylinder for 30 seconds. Switch the pump off. The reading on the left side of the cylinder is a direct readout of USgph. It is also designed to enhance the performance of chemical feed systems by providing a verification of the flow rate of the chemical feed pump.