Cartier’s first-ever mystery clock: the Model A – HK$6.87m (£687,000) at Bonhams Hong Kong.

Enjoy unlimited access: just £1 for 12 weeks

Subscribe now

The first of these were available in 1912 when even Cartier’s own sales team were in the dark as to how they worked. John Pierpont Morgan, Queen Mary and Joseph Stalin all clamoured to own one.

In fact, they operate in much the same way as the clocks created by the 19th century French illusionist Jean-Eugène Robert-Houdin.

Although the dial appears to float in a clear rock crystal case without mechanical parts, the movement is secreted in the base and the hands secured to revolving glass discs. However, in Cartier’s hands the form became synonymous with the Art Deco movement and became a staple of the brand over the decades.

This fine example, complete with original leather carrying case, was offered by the Mulloon Institute, a non-profit organisation in Australia working to combat the impact of climate change on agriculture.

After more than 50 competitive bids, it soared four times above its estimate to realise a premium-inclusive HK$6.87m (£687,000).