It was a mechanism for accurate measurement of sea distance and his paternity is attritubed to Archimedes.
It consisted of a box with co-operating gearwheels and a worm gear connected to a hydrokinetic winged wheel. The periphery of the wheel inside the wings touched sea level. The box was placed either on a float drawn by the ship or on the ship’s internal sidewall with the wheel shaft penetrating the inner sidewall. The wheel rotated according to the speed of the ship. A calibrated disc (within the box), incorporated into the shaft of the last gearwheel, indicated the distance travelled.