The no-deco scale is not a decorative element: it is a underwater safety tool engraved or printed on the rotating bezel of a dive watch, indicating the maximum time you can stay at a given depth without requiring decompression stops during ascent. The name comes from the English no-decompression limit, which is the threshold within which a diver can surface without following a protocol of intermediate stops to expel nitrogen dissolved in the bloodstream.
The scale structure is almost always a dual-ring design: the outer ring shows depth (in feet for US Navy versions, in meters for European versions), and the inner ring shows the permitted bottom time in minutes at that depth. Reading is direct and requires no additional calculations: you look at the maximum depth reached, follow the corresponding line, and read the remaining time. In water, with gloves and reduced visibility, this simplicity is as valuable as water resistance itself.
Doxa was the first manufacturer to systematically integrate a no-deco scale on the bezel of a production watch, starting with the SUB 300 in 1967, developed in collaboration with professional divers and based on US Navy tables. The shark-toothed ratcheted bezel — shark-toothed bezel — with patented no-deco scale became the industry's technical benchmark. Other manufacturers, including Jenny and Ollech & Wajs, adopted similar solutions in the following years. The Doxa Army model instead used the classic 60-minute scale, without decompression data.
From my workbench, I've witnessed considerable confusion over this term. Some sources use "no-deco" to simply indicate a bezel without graphic decoration, which is technically incorrect. Others apply it to any unidirectional bezel, confusing function with mechanics. The no-deco scale is a precise thing: a graduation derived from medical-military tables, not a stylistic choice. The Synchron Ti300M Poseidon, for example, features a unidirectional 120-click bezel with a no-deco scale, faithful to the original design.
An interesting and rare case: the 1985 Aqualand CQ-1012-50 printed no-deco tables directly on the strap, as a field reference stamped on the material. A solution I've never seen replicated elsewhere.