Chip log
INSTRUMENT USED TO MEASURE THE SPEED OF A SHIP AT SEA
Log (speed); Knot log; Knotted line; Patent log; Speed log; Taffrail log; Logreel; Log reel
A chip log, also called common log, ship log, or just log, is a navigation tool mariners use to estimate the speed of a vessel through water. The word knot, to mean nautical mile per hour, derives from this measurement method.