Historic documents giving an insight into an 18th Century clockmaker's struggle to be awarded the prize for measuring longitude have been bought by the National Maritime Museum.
The H4 marine chronometer resembled a large pocket watch
Working class joiner John Harrison was ridiculed when he suggested a clock could be used to accurately measure a ship's position at sea.
After 40 years of work, his H4 clock, tested in 1761, lost only five seconds in a period of just over six weeks - a remarkable accomplishment.
But he had a fight on his hands to persuade the Board of Longitude to give him the £20,000 reward offered in a 1714 Act of Parliament.
In the end King George III intervened on his behalf and Harrison was finally granted the money in 1772, aged 79.
Now papers belonging to the 2nd Viscount Barrington, who sat in judgement on Harrison's work, have been bought by the museum in Greenwich, south-east London.
Museum director Roy Clare said: "These fascinating papers will enable the museum's experts to reassess the discussions of the Board of Longitude and to shed new light on the events that led to Harrison eventually bypassing the board, and making a personal appeal to King George III for the longitude prize to be awarded to him."
The longitude problem, or how a ship could measure how far west or east it had sailed, led King Charles II to found the Royal Observatory in Greenwich, in 1675.
At the time it was believed the answer to the problem could be found in mapping the stars.
Sailors knew that for every 15 degrees travelled eastwards, the local time moved forward one hour and they could tell the local time from the Sun's position.
But they had no way of measuring time at a reference point such as Greenwich, as the motion of the sea made the pendulum clocks at the time hopelessly inaccurate.
The BBC made a documentary based on Harrison's memoirs
John Harrison spent 40 years developing a number of high-precision clocks that could handle the ups and downs of a voyage. His great breakthrough was the H4, which was carried on a sea journey by his son from Britain to Jamaica.
The remarkable "pocket watch", which measured 12 centimetres in diameter and weighed just over a kilogram, lost only five seconds on the voyage.
But the board thought it was a fluke and would not give him the prize money.
The notes made by Barrington show unofficial insights into the views and deliberations of the board, as well as revealing it was considering disbanding in the 1760s.
A rare unbound book published in 1765, which made the case for Harrison receiving the reward, has also been bought with help from the Heritage Lottery Fund and the Friends of the National Maritime Museum.
They will go on display at the observatory from 18 August, alongside Harrison's four famous timekeepers created between 1730 and 1759 which are on permanent display.