After four long and arduous years of unscrambling mathematical data, Radhanath Sickdhar had managed to find out the height of Peak XV, an icy peak in the Himalayas.
The mountain - later christened Mount Everest after Sir George Everest, the surveyor general of India - stood at 29,002 feet (8,840 metres).
Sickdhar's feat, unknown to many Indians, is now part of the Great Arc Exhibition in London's vibrant Brick Lane.
The Indian Government-sponsored exhibition celebrates 200 years of the mapping of the Indian subcontinent.
The exercise, which was called "one of the most stupendous works in the whole history of science" was begun by William Lambton, a British army officer, in Madras in 1802.
The survey involved several thousand Indians and was named the Great Trigonometrical Survey (GTS) in 1819.
Sickdhar, who was 39 when he made his discovery, was one of the survey's largely unsung heroes.
The man from Calcutta was called a "computer" since he worked on computation of data collected by survey parties.
He was promoted to the position of "chief computer" because of his good work.
It was first identified as a possible contender for the world's highest peak in 1847 when surveyors glimpsed it from near Darjeeling.
Sir George Everest found Sickdhar a rare mathematical genius
Several observations were recorded over the next three years by different survey parties.
But the announcement that it was the highest - thanks to Sickdhar's efforts - was delayed until 1856 as calculations had to be checked repeatedly.
Sickdhar, the son of a Bengali Brahmin, was born in October 1813 in Jorasanko, Calcutta's old city.