Beaufort Scale
A numbered scale from 0 to 12 that relates wind-force descriptions to defined wind-speed ranges and observable effects.
Force 0 is calm and force 12 is hurricane force, with named forces and speed bands between them. Descriptions of effects on the sea or land allow wind force to be estimated when a reliable instrument reading is unavailable.
Sir Francis Beaufort developed the scale for naval use in the early nineteenth century, and it was later standardised with quantitative wind speeds. Sea appearance also depends on fetch, duration, depth, current and swell, so observed waves do not always give an exact wind force.
