Calibre 551 — the certified chronometer with 24 jewels

In brief

More than a million certified examples left Omega between this calibre and the 561. The 551 is the no-date half of the pair: a 550 refined to 24 jewels and put through official chronometer testing, and one of the most admired movements the company has made.

Short history

1959 brought the 551 and, with a date, the 561 — both certified as chronometers. Between them they account for more than a million certified examples, and they are probably the most admired run of movements in Omega's history.

Why it matters

Alongside the 561, this is one of the most highly regarded automatics in Omega's twentieth-century catalogue: accuracy certified at the factory, and a reliability that still holds up today after a proper service.

Watches that used it

• Constellation chronometer
• Seamaster (high-end models)