First produced in 1932, Calibre 281 is part of a family of important chronograph movements, including the first ever wristwatch chronograph with a calendar complication. These movements were produced with Martel and shared with Zenith. They featured Martel's variable diameter technology, which used larger plates to increase the size of the movement from 12 ligne to 13.5 (also called 14) ligne.
There were many variants on the basic Cal. 281 movement, and production lasted more than half a century. All were 4.58 mm high but diameter varied from 12 ligne to 13.5 ligne. All beat at 18,000 A/h and ran for 36 hours. The Cal. 38x variants have a flat hairspring rather than Breguet. There were also later Cal. 48x versions.
Zenith named their versions of these calibres for their size in ligne.