Summary: "Prototype tests of an acoustic flowmeter system were made in a 24-ftdiam power penstock at Oahe Dam to evaluate the system prior to permanent installation in the outlet works at Summersville Dam. Comparative discharge measurements included acoustic, penstock pressure-momentum (Gibson), turbine model test ratings, scroll-case pressure differential (Winter-Kennedy flowmeter), and surge tank volume changes. The acoustic flowmeter measurements were very consistent and many of the comparisons were within 1%. The location of the measuring section for a single-path acoustic flowmeter must be selected to give a known or measurable relation between the flow pattern of the whole section and that along the acoustic path" (p. xi).