A 14th Century scientific instrument uncovered during building work has been given an auction guide price of between £60,000 and £100,000.
The astrolabe quadrant - described as the "pocket calculator" of its age - was found in Canterbury, Kent, in 2005.
Made in England and dated back to 1388, the device was used for telling the time, mapping the stars and making height and depth measurements.
It is due to be sold at Bonhams in London on 21 March.
The auction house said it was one of only eight known examples in the world today.
The brass instrument was found during excavations for a restaurant extension in Canterbury.
Bonhams said: "There it lay beneath a series of clay floors, inside a sealed soil deposit dated to circa 1375-1425."
The site of the find is known as the House of Agnes, a 17th Century inn on the main road out of Canterbury to London.
Ellie Dekker, an expert on astrolabe quadrants, said: "Finding a complete scientific instrument during archaeological work is very rare, but finding an instrument that was used only by scholars well versed in the secrets of the sky is exciting."