You may well have clocked this clock at Bethnal Green. But it's not the only timepiece decorated with the tube roundel. Here, we take the time to track them all down.
Four stations feature the clocks, which were designed by the Magneta Time Company in the late 1940s. They were installed along the eastern extension of the Central line when it became operational from 1946 (having previously served as air-raid shelters and a bomb-proof munitions factory... but that's another story). Here's where to find them...
Perhaps the best known roundel clocks — and certainly the closest to central London — are to be found on the two platforms at Bethnal Green.
Here, the clockface is set within a brass rim, giving the appearance of a giant pocketwatch. The roundels and hands are picked out in matching metal.
Five stops east and we reach Wanstead. Its twin clocks hang side-by-side, at the foot of the escalators. Functional redundancy — why would anyone need to see two clocks? — but it looks rather handsome. [Update 24 Feb 2020] Some insight has now been offered by reader Nigel Pitt:
"When I moved to Wanstead ten years ago I realised that they were missing from the platforms. I made some enquiries and found that they had been removed while a refurb was taking place, but never returned (as had been specified). Unfortunately for some reason they could not be re-installed on the platforms so a compromise was necessary."
The quirky alignment means that Wanstead — very probably — is the station where the greatest number of roundels (26) can be captured in one photograph, anywhere on the network.
If the Bethnal Green clocks look like pocket watches, the simple black-and-white design at Wanstead is more reminiscent of a giant alarm clock.
One stop along, and the clocks at Redbridge look near-identical to those at Wanstead. This time, though, we're back on the platforms.
One final hop brings us to Gants Hill — a remarkable station noted for its Moscow-inspired lower concourse. The clocks here are the most colourful on our short tour, with roundels in red and blue. Lovely.
And some bonus clocks
Chadwell Heath: A fifth station is set to join this exclusive, horological club. As part of its ascension to the Elizabeth line, Chadwell Heath station is set to get a replica roundel clock. The Chadwell Heath South Residents' Association has secured a grant to commission a pair of the clocks from royal warrant holders HS Walsh & Sons.
Hammersmith: Another tube-themed clock can be found at Hammersmith station. Rather then riff on the roundel, this one instead uses the familiar colours of the Piccadilly and District lines, served by the station, with bars and circles reminiscent of those from the tube map to mark the hours.
Tooting Broadway: This Northern line station houses a more traditional clock, which some have likened to the shape of a roundel. South Wimbledon has something similar.
Wikipedia has a photo gallery of even more clocks on the underground, but no others with roundel or tube map connections.