The current Datejust 31 in dark grey, with box and papers.

The Datejust 31 is the mid-size of the watch Rolex built its reputation on: the first self-winding wristwatch with a date that changed at midnight, launched in 1945, and made ever since in a 36mm Oyster case with a screw-down crown, an automatic chronometer movement, the date under its Cyclops lens at three, a fluted, smooth or engine-turned bezel, and a Jubilee or Oyster bracelet. Because Rolex made it for eight decades in every dial and metal, the pre-owned market is deep and this is where the money goes when people search for a Rolex that is not a Submariner.

Rolex redesigned the Datejust 31 in 2018 as the 278xxx series with the calibre 2236, the first Rolex movement with a silicon hairspring, and the 278240 is the all-steel one with a smooth bezel on an Oyster bracelet. Dark grey sunray is the dial that makes it read as a men’s watch on a woman’s wrist or a small watch on a man’s; it is the least expensive current Datejust with papers on this page, and it is sized long, so ask about the removed links.

WGACA gives the reference as 278240, the size as 31mm, the case as steel with a smooth bezel and sapphire, the movement as quickset automatic, the dial as dark grey with baton markers, the bracelet as an Oyster band with Oysterclasp, box and papers as included, a serial, the wrist as 7.5 to 10 inches and the condition as Excellent with faint scratching. The photograph matches; the calibre 2236, its certification, reserve and 100 metres are Rolex’s published figures for the 278240.

WGACA authenticates in-house and is not a Rolex authorised dealer, and Amazon adds its 30-day return window. Ask for the serial, whether box or papers come with it, and when it was last serviced. Nothing here was measured on the watch.

This unit is sold by What Goes Around Comes Around (WGACA) through Amazon Luxury Stores, authenticated by the seller with Amazon’s 30-day return window on top; it is one piece, and when it sells the listing goes away, so the second button opens the live search for 31mm Datejusts.

Steel and two-tone Datejusts have resold close to what pre-owned buyers paid, sometimes more, sometimes less; that is a pattern, not a promise, and nothing here is investment advice.