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-powered vehicle exceed that of the wind, both directly "into the wind" and directly "downwind" by transferring power through a drive train between the rotor and the wheels. The wind-powered speed record is by a vehicle with a sail on it, "Greenbird", with a recorded top speed of . Other wind-powered conveyances include sailing vessels that travel on water, and balloons and sailplanes that travel in the air, all of which are beyond the scope of this article. Sail-powered vehicles travel over land or ice at apparent wind speeds that are higher than the true wind speed, close-hauled on most points of