The acoustical method designated Stamni, which may be used for the measurement of Mach number, true airspeed and true air temperature, has been under development by the author and his coworkers since 1946. Under a null balance condition the Mach number is measured in direct proportion to a length. The ratio of this length to a measured acoustic transit time represents true airspeed, while the transit time itself determines true air temperature. For some time Stamni operating principles have been based entirely upon ray acoustics, and have received experimental confirmation only over part of the subsonic velocity range. Recently, however, Stamni operation has been studied intensively in terms of acoustic field theory, starting with the work of Miles. Conclusions based upon ray acoustics are found, in general, to be well substantiated. Complete solutions for the supersonic velocity range contain contributions from advanced as well as retarded velocity potentials. In agreement with the analysis of ray acoustics, Stamni measurements in this range appear to be possible only if the terms associated with advanced velocity potentials are attenuated by emitter directivity. Comparative viewpoints of ray acoustics and field theory are presented.