Knot (unit) fluids (tidal streams, river currents and wind speeds) are also measured in knots. Thus, speed over the ground (SOG) (ground speed (GS) in aircraft) and rate of progress towards a distant point ("velocity made good", VMG) are also given in knots. Until the mid-19th century, vessel speed at sea was measured using a chip log. This consisted of a wooden panel, attached by line to a reel, and weighted on one edge to float perpendicularly to the water surface and thus present substantial resistance to the water moving around it. The chip log was cast over the stern of the
Wind transducer Wind transducer A wind transducer is a device used by sailors to receive a real-time measurement of wind speed and direction. A wind transducer is usually mounted on the masthead of a sailing boat and is occasionally used by power boats too. The wind speed and direction measurements are more critical to sailing boats than to power boats. Sailors rely on the wind speed and direction to help with navigation and pilotage. These devices can be calibrated to measure the true wind speed and the apparent wind speed (speed that a sailor would 'feel'). Sailing boats can sail at a