This standard describes the various types and classes of cold water displacement meters with bronze main cases, in sizes 1/2 in. (13 mm) through 2 in. (50 mm), and the materials and workmanship employed in their fabrication. The displacement meters described, known as nutating disc or oscillating piston meters, are positive in action because the pistons and discs displace or carry over a fixed quantity of water for each nutation or oscillation when operated under positive pressure.