Audemars Piguet introduced the perpetual calendar complication to the Royal Oak collection in 1983 with Ref. 5554 (later designated as the Ref. 25554). Back then, this was seen as a bit of a bold move – a high complication like the perpetual calendar was seldom presented in a sports watch.

The Ref. 25829TA is another example of Audemars Piguet pushing the envelope when it comes to case materials – the present watch is in two-tone metal. It features tantalum, a hard lustrous grey metal, with contrasting 18k yellow gold accents. Tantalum is a hard and expensive metal used extensively in aeronautical and medical industries. Hard to machine, it is highly resistant to corrosion and wear and has a distinct greyish blue lustre.

The result is a strikingly good-looking Royal Oak with a skeletonized perpetual calendar dial. The bracelet has a steel clasp featuring the stamps of Gay Freres, the celebrated bracelet maker. According to Audemars Piguet, the skeletonised Royal Oak perpetual calendars were made in a handful of configurations besides tantalum and yellow gold; they were also made in tantalum and pink gold and platinum and pink gold. All combinations featured a maximum production of just 15 pieces. The caseback features the number 28, this is the ‘Royal Oak’ number, not to be confused with the limited-edition number.