Sigismund Rentzsch gold watch – estimate €3000-7000 at Dr Crott on May 22.

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In 1811 he became a British citizen. Two years later he patented a keyless pocket chronometer, much admired by his contemporaries. From 1821 until his death in 1843, he was accredited as watchmaker to the royal family.

Very few of his watches have survived; all have unusual features, such as repeating mechanisms or complicated escapements.

This also applies to a gold watch with engine turned dial on offer at Dr Crott in Mannheim on May 22. It is fitted with a spring detent escapement and a rare type of temperature compensation, the so-called ‘sugar tongs’, most probably invented by the chronometer pioneer Thomas Earnshaw. Estimate €3000-7000.