A chart to help determine the strength of the wind by its effect on the surrounding environment, such as the height of sea waves or the movement of tree branches. It was introduced by British admiral Francis Beaufort in 1806, to help sailors objectively determine wind strength. Later, the effects of wind on land and wind speed were added to the scale. In the 20th century, five additional grades were added to the original range of 0—12 to denote tropical typhoons.