A pioneering Kent calculating machine is being exhibited for the first time this week.

The extremely rare device is being moved from its home at Chevening House to be exhibited at the Winter Fine Art & Antiques Fair at Olympia, running until Sunday.

The calculator will be shown with a Thomas Gainsborough portrait of its inventor Earl Stanhope and a collection of plans and drawings of the calculator. It will be moved from Chevening House near Sevenoaks, which is the official country residence of the Foreign Secretary David Miliband.

Mick Byrne, manager from Crown Fine Arts, which is moving the device, said: “This is a momentous move as it is believed that this is the first time that the calculator has left the house since the 3rd Earl’s death in 1816.”

The calculator was invented by the extraordinary and colourful Charles, 3rd Earl Stanhope (1753-1816) and will be exhibited at the 16th annual Winter Fine Art & Antiques Fair, courtesy of the Trustees of the Chevening Estate.

So how does it work?

Earl Stanhope’s “arithmetical machine” solved problems in multiplication and division by the revolution of a small winch. It was the world’s first calculating machine to tackle the tens carry mechanism and is a marvel of 18th century ingenuity. One of only two surviving examples, the machine - which was made and cased by James Bullock in c 1777 - is seen as a forerunner today’s computer.