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The signed perpétuelle, self-winding watch No 217 offered at the auction on May 16, had a day and month calendar and was one of only 15 to feature Breguet’s ‘equation of time indicator’ – the difference between mean time and solar time.

The estimate was SFr$600,000-1.2m.

In 1800 Breguet sold it for Fr3400 to Napoleon’s general, and later rival, Jean Victor Moreau. After the general’s death in 1813 he bought it back, gave it a fashionable guilloché silver dial by Tavernier and, in 1817 sold it for FR4800 to banker Charles Louis Havas.

Historic exchange rates can be misleading but in 1817, a franc weighed just shy of 1 troy ounce of gold - giving an approximate value of £3m in today's money.

More recently, in 1965 the watch took £8500 at Sotheby’s in London.

The top auction price for a Breguet watch was the SFR3.8m (then £2.62m) taken at Christie’s Geneva in May 2012 for a signed two-movement 1814 watch No 2667.