an instrument for measuring the velocity of flowing water. The instrument’s action is based on the relation between the velocity of the flowing water and the number of rotations of the cups or vanes that are placed in the moving current. The number of revolutions made by the cups or vanes is transmitted by an electrical signalling system to an observer or is registered on a mechanical meter attached to the body of the instrument. There are many different models of current meters; some measure the velocity and the direction of the water flow, and others measure the magnitude of the projection of the velocity of the current on the direction of the axis of the current meter (component current meters). The relation between the number of rotations and the velocity of the water is fixed for each current meter by calibration. A current meter is useful for measuring the velocities of flow from 0.03 to 10-12 m/sec.