The document describes the Lutron DO-5509 digital dissolved oxygen meter, which features a polarographic probe for precise measurement of dissolved oxygen and temperature. It has a measurement range of 0 to 20.0 mg/l with an accuracy of ± 0.4 mg/l, and is suitable for various applications including aquariums, medical research, and water conditioning. The meter includes accessories such as a carrying case, operation manual, and spare probe components.