File:Detailed view on chronograph pushers and crown (with open watch movement) of an Omega Cal. 1861 chronograph movement from an Omega Speedmaster (cropped).jpg - Wikimedia Commons
Omega Speedmaster Professional Moon Watch - Hesalite
The Naked Watchmaker
Omega Speedmaster Movements: 1861 vs. 1863 - Bob's Watches
Watch Service: Omega Speedmaster Professional. Cal 1861. (The Moon Watch) – The Watch Professional
Ron Gordon on LinkedIn: Omega caliber 1861 (base movement Lemania 1873) is a manual-wind…