Few movements or many

The clearest difference between the two is not on the dial. Rolex builds its entire catalogue on a handful of calibers: five of them, the 2236, 2235, 3155, 3135 and 3255, power 78 per cent of the 3,659 Rolex watches here, and every one of them is automatic. Omega's five most common calibers cover 38 per cent of its 3,794, and the list runs to 177 movements, 23 per cent of the watches quartz and 7 per cent hand-wound.

That is a difference of philosophy. Rolex changes a movement rarely and then everywhere at once, which is why the 3135-to-3235 piece can describe a whole generation in one comparison. Omega builds families around an escapement: the co-axial escapement of 1999 on an ETA base, then the in-house 8500 of 2007, then the Master Chronometer versions certified by METAS from 2015, which the Master Chronometer piece sets out. Rolex's answer is the Superlative Chronometer, its own test of the cased watch to two seconds a day.

What the cases say

Half of the Rolex watches here are solid gold or platinum and a further 36 per cent are Rolesor, steel with a gold bezel; only 8 per cent are plain steel. Omega is the reverse, 45 per cent steel and 28 per cent precious metal. The Rolex median case is 36 mm, because the Datejust family, five collections from the Lady-Datejust to the Datejust 41, is 60 per cent of the catalogue; Omega's median is 38 mm, with 41 mm and 42 mm the most common sizes.

Water resistance follows the case. 98 per cent of Rolex watches are rated to at least 100 m, because almost every Rolex is an Oyster, against 61 per cent of Omegas; but Omega goes deeper, with 15 per cent of its watches rated to 300 m or more against 2 per cent of Rolex. Only 1 per cent of Rolex watches here have a display back; 49 per cent of Omegas do.

Complications and rarity

Omega makes more of them. 21 per cent of its watches are chronographs, against 5 per cent of Rolex, where the Daytona is the only one; Omega also carries annual calendars, world timers and tourbillons the Rolex catalogue does not attempt. Rolex's complications are the Day-Date, the Sky-Dweller and the GMT-Master.

Neither makes limited editions the way the rest of the industry does. Rolex's share here is three watches of 3,659, which rounds to none; 8 per cent of Omegas are numbered. The rarity medians are 5 for Rolex and 4 for Omega, and 14 and 18 per cent of their scored watches sit at 8 or above; the variant-families piece explains why the reference-number conventions of the two make that comparison approximate.

The direct pairs

Where the two ranges meet, the library has both sides. The Submariner and the Seamaster Diver 300M are the 300 m divers, 52 and 274 references. The Datejust 36 and the Aqua Terra are the everyday watches with a date, 519 and 579. The Daytona and the Speedmaster Moonwatch are the chronographs, one automatic on the 4130, the other hand-wound on the 3861. Each collection page lists every reference and the caliber pages every watch that carries one.