Omega Speedmaster Moonwatch Professional 3861 Hesalite 310.30.42.50.01.001Overview The Calibre 1861 a hand wound movement derived from the Lemania bauche powered the Moonwatch for over four decades with minimal change. The 310. 30. 42. 50. 01. 001 introduced the 3861: the same hand wound architecture, but with Omega's Co Axial escapement, METAS Master Chronometer certification, and magnetic resistance rated to 15,000 gauss. This Hesalite example represents the historically accurate configuration acrylic crystal, solid