The Welshman was largely responsible for completing the section of the Great Trigonometric Survey of India along the meridian arc from the south of India extending north to Nepal , a distance of approximately 2500 mmeters urvey was started by William Lambton in 1806 and lasted several decades .
The Welshman was largely responsible for completing the section of the Great Trigonometric Survey of India along the meridian arc from the south of India extending north to Nepal , a distance of approximately 2400 kilometres . 
 The survey was started by William Lambton in 1806 and lasted several decades .