Omega Speedmaster Chronograph Professional Caliber 861 42mm Hesalite Vintage Year 1976 Speedy 145022-76 ST | Sansom Watches, Rolex, Breitling, Omega, and more
Omega Speedmaster Moonwatch “Pre-Moon” Caliber 861 Manual Wind | Value Your Watch
OMEGA Speedmaster: The Evolution of Calibers 321 and 861, by Bernhard Stoeber — Horological Society of New York