Constellation Co-Axial 27 Brushed Stainless Steel / Diamond / White MOP

In Context

At 27 mm this is jewellery scale — a watch sized to be worn as an ornament rather than read across a room. The case back is open, so the movement is visible without taking the watch apart, and the sapphire crystal will resist everything short of deliberate abuse. 100 m is genuine swimming resistance — more than the shape of this watch suggests it would need.

The movement winds itself from the motion of your wrist. 50 hours of reserve is enough to set it down on Friday evening and find it still running on Monday. At 25,200 vph the seconds hand advances 7 times a second.

123.15.27.20.55.003 stands on its own in this catalogue — no other reference here shares its base number. It pairs a white dial with a stainless steel case.

The 8520 is Omega's co-axial caliber for ladies' and mid-size cases, introduced in 2010 with the Ladymatic. It powers 193 watches in this library. It brought the escapement and the in-house architecture of the [8500](/calibers/omega-8500) down to a size for 27 mm to 34 mm cases: a co-axial escapement, a free-sprung balance with the Si14 silicon balance spring, bidirectional winding, 28 jewels and a 50-hour reserve at 25,200 vph, certified by the COSC. The [8521](/calibers/omega-8521) is the same movement with a red gold rotor and balance bridge for gold-cased watches. In the library it powers 65 [Constellations](/brands/omega/constellation), the 27 mm and 31 mm Co-Axial models, 61 [Ladymatics](/brands/omega/ladymatic), 54 [Aqua Terras](/brands/omega/aqua-terra) at 30 mm and 34 mm and 13 [Planet Oceans](/brands/omega/seamaster-planet-ocean) at 37.5 mm. The 34 mm case accounts for 93 references and the 27 mm for 44. The [8700](/calibers/omega-8700) is the Master Chronometer movement that replaced it in the smallest cases in 2018, and the [8800](/calibers/omega-8800) its counterpart from 34 mm up; the glossary covers the [co-axial escapement](/glossary/co-axial-escapement).

192 other watches in the library run the Omega 8520.

Omega

LadyMatic Co-Axial 34 Stainless Steel / Red Gold / MOP / Bracelet

425.20.34.20.55.001 · 34 mm

Omega

Seamaster Aqua Terra 150M Master Co-Axial 34 Stainless Steel / Yellow Gold / MOP / Bracelet

231.20.34.20.55.002 · 34 mm

Omega

Seamaster Aqua Terra 150M Co-Axial 30 Stainless Steel / Yellow Gold / Diamond / MOP / Bracelet

231.25.30.20.55.004 · 30 mm

Omega

Constellation Co-Axial 27 Brushed Stainless Steel / Yellow Gold / MOP

123.20.27.20.55.003 · 27 mm