Dissolved Oxygen Meter is used for determining oxygen content of aquarium water and waste water by using polarographic electrode. This apparatus consists of mechanical barometric pressure and salinity compensation arrangement. It can automatically compensate temperature to maintain its accuracy of measurement when temperature fluctuates. Its expandable memory can store sufficient measurement data. USB communication interface of this Dissolved Oxygen Meter promotes easy transfer of data to computer.  Large display screen of this system shows temperature level, measured amount of dissolved oxygen and output current simultaneously.