Douglas sea and swell scale either of two arbitrary series of numbers from 0 to 9, used separately or in combination to define qualitatively the degree to which the ocean surface is disturbed by fresh waves (sea) generated by local winds, and by decaying waves, or swell, propagated from their distant wind sources (see Table (Douglas sea and swell scale)). The scales were devised in 1921 by the British Navy captain H.P. Douglas and were adopted by the International Meteorological Conference in Copenhagen in 1929.