73 / | HD | MEASURING AND TESTING |
861 | DF | VOLUME OR RATE OF FLOW {23} |
861.18 | DF | .~ By measuring vibrations or acoustic energy {5} |
861.27 | DF | .~.~ Transit time of acoustic waves {2} |
861.28 | .~.~.~ Transmitted along single path {1} | |
861.29 | DF | .~.~.~.~> In both directions simultaneously |