You searched for: “electromagnetic log
electromagnetic log, EM log
1. An instrument used to measure and to record the movement rate of a vessel through water, having an electromagnetic sensing element that hangs from the vessel (craft designed for water transportation) and which produces a voltage that is directly proportional to the vessel's speed.
2. A log containing an electromagnetic sensing element extended below the hull of a vessel or ship.

This device produces a voltage directly proportional to the speed through the water.

This entry is located in the following unit: electro-, electr-, electri- (page 40)