An incredibly rare 14th Century scientific instrument has sold for a world record price at Bonhams in London.
The astrolabe quadrant - described as the "pocket calculator of the 14th century" - was bought by an anonymous telephone bidder for £138,000, including buyer's premium.
It had been expected to sell for between £60,000 and £100,000, but exceeded expectations.
The instrument was able to measure the height of a building, the depth of a well, or accurately date when the next Easter moon would fall.
It was made in England in 1388 and is one of the oldest and smallest in existence.
Jon Baddeley, Bonhams: "It is extraordinarily rare to find a scientific instrument of such an early date and impeccable provenance at auction."
Jon Baddeley, director of Scientific Instruments for Bonhams, said: "It was a privilege to handle such an historically important artefact.
"It is extraordinarily rare to find a scientific instrument of such an early date and impeccable provenance at auction."
The quadrant, one of only eight examples known in the world, was discovered during excavations for a restaurant extension in Canterbury, Kent, in 2005.
The site of the discovery is known as the "House of Agnes", a 17th century inn on the main road to London, just beyond the Westgate of the city.
Bonhams said: "There it lay beneath a series of clay floors, inside a sealed soil deposit dated to circa 1375-1425."
It has two sight vanes on one edge and there is a suspension with a hole for a silken cord with a bead on the front of the instrument.
On its back, two concentric circles with calendar data can be seen, with an eagle sitting in the centre of the rings.
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