Improved performance, enhanced user-interfaces, and reduced cost-of-ownership have helped thermal mass flowmeters gain acceptance in the industrial process control market for gas flow measurement as shown in the Principle of Operations & Applications publication. Part I provides a comprehensive explanation of thermal principle of operation. It also compares the performance and cost-reduction attributes of the industrial thermal mass flowmeter to those of other flow monitoring instruments. Part II includes a description of the various sensors, flow body and electronic configurations available and a list of typical applications.