All too often a cool concept comes along, makes a splash and then immediately disappears under the water, never to emerge again. Thank god that’s not what happened to Audemar Piguet’s Royal Oak concept, the RD#2, which debuted last year. After a little extra development, the world’s thinnest perpetual calendar is back and into production with the Royal Oak Selfwinding Perpetual Calendar Ultra-Thin.

Despite the restrictions of needing to make this an actual production watch, the thinness remains the same as the original concept at just 6.30mm. That’s a moon phase, day, date, month, leap year and local time in a watch way thinner than whatever you’re wearing right now – and in a Royal Oak case at that.

One of the biggest changes between the concept and this new version is the case. Previously it was a fully platinum beast, making it one of the heaviest ultra-thin’s you could find. Now the precious metal has mainly been swapped out for titanium with a few platinum touches here and there. Needless to say, it wears a lot more comfortable.

It’s not just the wearability that’s changed either but the legibility. The concept has a classic petite tapisserie you see on many a Royal Oak, lovely but not the easiest thing to read so many counters off. Now, that guilloche been swapped for a more minimal matte finish, creating a much cleaner, clearer dial.

Inside it all is the new 5133 calibre, a completely redesigned ultra-thin calibre that strips out every unnecessary component possible, no mean feat in something as complex as a perpetual calendar. It boasts a 40-hour power reserve, though like any perpetual calendar you’ll want to make sure it doesn’t wind down. Setting them is a pain.

Despite swapping platinum for titanium, the new Royal Oak Selfwinding Perpetual Calendar Ultra-Thin still commands a heft investment, priced at CHF 140,000 (just over £110,000). Still, for any world record-holding timepiece that’s not so bad; for a world record-holding Royal Oak it’s all but expected.

Price & Specs:

Model Name: Audemars Piguet Royal Oak Selfwinding Perpetual Calendar Ultra-thin

Ref: 26586IP.OO.1240IP.01

Case/Dial: 41mm diameter x 6.30mm height, brushed titanium, polished 950 platinum bezel and links, titanium screw-locked crown

Movement: In-house Audemars Piguet Cal. 5133

Power Reserve: 40h

Frequency: 36,000 VpH (5 Hz)

Functions: Hours, minutes, perpetual calendar with day, date, astronomical moon, month, leap year, night and day indication

Water Resistance: 20m (2 ATM)

Strap: Satin-brushed titanium bracelet with polished 950 platinum links and titanium AP folding claps

Price & Availability: CHF 140,000 (excl. taxes), boutique piece only

More information at Audemar Piguet’s website.