This 2017 edition of Gas Measurement Manual, Part 4, Turbine Meter, is the revision of the 1985 edition. Substantial changes have been made and vastly expanded to incorporate the latest industry knowledge on turbine meter technology. The manual is primarily for training engineers, technicians, and other personnel who are new to gas flow measurement. It describes the theory of operation, operating characteristics and applications, as well as installation specifications, calibration, testing and maintenance procedures. Examples of calculations of flow by axial flow turbine meters are also included.