A Dumas Neyrpic water current meter with propeller, made in  France. This horizontal-axis instrument is used for measuring water velocities between 0.2 and 2.4 metres/second. An array of these devices can be used for hydroelectric turbine flow measurements. A single device can be lowered on a wading rod and used to measure flow in a stream or an ocean current.  The number of the revolutions of the propeller is proportional to water velocity and is counted electronically. This style of instrument has a cosine response to off-angle water currents.
<a href="//commons.wikimedia.org/wiki/User:Wtshymanski" title="User:Wtshymanski">Wtshymanski</a>
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