Beaufort scale

Beaufort scale is a scale of measuring wind speed. It was devised by the English admiral and naval hydrographer Sir Francis Beaufort (1774 — 1857), and hence was named after him. This measure is based on a visual estimation of the effects of the wind ranging from force 0 to 12. Force 0 is less than 1 knot or 1mph speed, which is considered calm. Force 12 is 64 knots speed or above, ie 74 mph and above, which is categorized as "hurricane".