Long before the Speedmaster made the calibre 321 famous, Omega was already using the movement in a generation of remarkably sophisticated wrist chronographs. Introduced in the late 1940s, the ref. 2451 combined a compact approximately 35mm stainless steel case with round pump pushers, a screw-down case back and the manually wound column-wheel chronograph movement that would later become inseparable from Omega's professional chronographs. This example adds an especially evocative period detail with a so-called “telephone timer” dial, designed around the way telephone calls were once charged in timed increments.

Against the warm cream-coloured dial is an outer tachymeter scale, applied Arabic 12 and three recessed registers. Most distinctive is the 30-minute chronograph counter, where elongated markings at three, six and nine minutes allowed the wearer to follow the billing intervals of a telephone conversation at a glance. It is a wonderfully specific reminder of an era when a chronograph could be a genuinely useful everyday instrument. Inside is Omega's calibre 321, descended from the 27 CHRO C12 architecture and featuring the traditional column-wheel construction that would subsequently power the earliest Speedmasters.