Omega cal 3861

The cal 3861 replaced the 1861 in the current Speedmaster Moonwatch Professional, adding the Co-Axial escapement, a free-sprung balance with a silicon balance spring, and METAS Master Chronometer certification to the iconic manual-wind chronograph platform. The chronograph itself is unchanged in principle: cam-actuated with a lateral clutch, as it has been since the cal 861 replaced the column-wheel cal 321 in 1968. It is anti-magnetic to 15,000 gauss and rated to plus or minus 0/plus 5 seconds per day in the cased watch. A central bridge layout was retained to keep the familiar caseback view.