 Under laboratory conditions the Parshall flume - upon which the Montana is based - can be expected to exhibit accuracies to within +/-2%, although field conditions make accuracies better than 5% doubtful.The Montana Flume is a restriction with free-spilling discharge that accelerates flow from a sub-critical state (Fr~0.5) to a supercritical one (Fr>1).The free-flow discharge can be summarized as

Where

Montana flume discharge table for free flow conditions