This publication represents a basic standard for safe operation, and substantial and durable construction for diaphragm-type gas displacement meters having a gas flow rating of 500 cubic feet per hour capacity (14.16 m3/h) and over at 0.5-inch water column (125 Pa) differential pressure at base conditions. This work is the result of years of experience, supplemented by extensive research. The standard is designed to help ensure efficient performance and substantial construction of equipment.