Douglas Sea State Scale
F5. The Reference Layer: Glossary, Units, Signals and Information SourcesDefinition
Sea-state scale developed by Sir Henry Percy Douglas in 1917.
The Douglas sea state scale, set out by H. P. Douglas in 1921, codes the sea surface in two parts: state of sea (wind sea) 0 to 9 and swell separately, each tied to wave height bands. Sea state 0 is glassy calm; state 4 is moderate at 1.25 to 2.5 m; state 9 is phenomenal above 14 m. It is the scale logged in deck and weather observations and reported in synoptic codes, distinct from the Beaufort wind scale, which measures wind force rather than the resulting sea.
Source: Douglas sea state scale (1921)