Nain Singh Rawat (1830–1882) was an Indian explorer and surveyor known for his remarkable contributions to the Great Trigonometric Survey of India during the 19th century. Born in the Johar Valley of Kumaon in present-day Uttarakhand, Nain Singh became one of the most renowned Indian explorers of his time.

Nain Singh’s significant achievements include his exploration of the uncharted territories of Tibet and Central Asia. He embarked on a series of perilous journeys, often undercover, to gather geographical and cartographic information for the British authorities. His ability to collect data with precision, even under challenging conditions, earned him recognition and respect.

One of Nain Singh’s most notable expeditions was his journey to Lhasa, the capital of Tibet, during 1865-1867. Disguised as a Tibetan trader, he meticulously measured distances, recorded geographical features, and gathered valuable information about the region. Nain Singh Rawat’s legacy endures as a pioneering figure in the history of exploration and cartography in the Indian subcontinent.

Radhanath Sikdar (1813–1870) was an Indian mathematician and surveyor who played a crucial role in the measurement of the height of the world’s highest peak, Mount Everest. Born in Kolkata, Sikdar was largely self-taught and developed a keen interest in mathematics and surveying from an early age.

In 1852, Sir George Everest, the Surveyor General of India, initiated the Great Trigonometric Survey of India to accurately measure the heights of the Himalayan peaks. Radhanath Sikdar, who was working as a computer (assistant) in the survey, made a significant contribution to this ambitious project. Using trigonometry and geometry, Sikdar calculated the height of Peak XV, which would later be recognized as Mount Everest.

Radhanath Sikdar’s work laid the foundation for subsequent measurements of Mount Everest and significantly contributed to the understanding of the world’s highest mountain. His dedication to precision and mathematics has left a lasting impact on the field of surveying and the exploration of the Himalayas.