This year, Revolution turns 20. Two decades of chronicling watches, people and ideas have given us a front-row seat to a remarkable story: how an age-old craft has both preserved its soul and reinvented itself for the 21st century. To celebrate, we’ve chosen over 100 names and milestones that, for us, define the era so far. From leaders to watches, you can see the whole list here.

When Audemars Piguet revealed the Royal Oak RD#2 Perpetual Calendar Ultra-Thin in 2018, it was presented quietly as a research project. By the time the production version appeared in 2019, it was clear that the watch marked one of the most important technical breakthroughs of the past two decades. The Royal Oak had already cemented its place in design history; with the RD#2, it did the same in mechanical innovation.

The challenge was simple to state but fiendishly difficult to solve: create the thinnest self-winding perpetual calendar ever made. Perpetual calendars, by nature, are complex machines, layering cams, levers and wheels to track the shifting months and leap years. Traditionally, this complexity came at the cost of thickness. Audemars Piguet’s engineers set out to do the opposite.

Audemars Piguet Royal Oak RD#2 Perpetual Calendar Ultra-Thin

The solution came not from miniaturizing individual parts but from re-thinking the entire architecture. Instead of stacking functions in layers, they flattened them into a single plane. Month, leap year, day, date and moonphase — all were integrated directly into the base caliber. This required redesigning three traditional movement levels into just one, reducing the thickness from more than 7mm in earlier AP perpetuals to an astonishing 2.89mm in the RD#2. With the case at just 6.3mm, the result was the slimmest automatic perpetual calendar in history.

The achievement was more than numbers on a spec sheet. By integrating complications into a unified caliber, Audemars Piguet demonstrated a new approach to movement design, one that could influence generations of watchmaking. It was not a compromise — the perpetual calendar remained perfectly legible, with balanced subdials and the classic moonphase at 12 o’clock. Nor was it fragile: the movement was built to be robust enough for daily wear, even within the famously sporty Royal Oak.

The classic moonphase at 12 o’clock

In a landscape where many innovations feel incremental, the RD#2 stood out as a genuine leap forward. It reminded the industry that even in a watch as recognizable as the Royal Oak, there is still room for real invention. For Audemars Piguet, it confirmed a truth the brand has lived by since its founding: that pushing technical boundaries is as vital to legacy as preserving design codes. In distilling one of horology’s most revered complications into its thinnest form, the RD#2 didn’t just set a record. It set a new benchmark for what modern watchmaking could be.

Tech Specs: Audemars Piguet Royal Oak RD#2 Perpetual Calendar Ultra-Thin

Movement: Self-winding Caliber 5133; 40-hour power reserve
Functions: Hours and minutes; perpetual calendar with moonphase display
Case: 41mm × 6.3mm; platinum (launch version) or titanium/ platinum mix (production version); water resistant from 20m
Dial: Satin-brushed blue
Strap: Satin-brushed bracelet in matching metal