Above: As the Great Trigonometrical Survey continued to extend east and west, pundits were used to obtain vital information in forbidden territories. Nain Singh used this compass and prayer wheel to record survey information for a map of the Yarlung Zangbo region in Tibet, published in 1874 in the Journal of the RGS.

Right: Lambton’s Great Theodolite, used by both William Lambton and George Everest during the Great Trigonometrical Survey of India, was capable of measuring both the vertical and the horizontal axes. It weighed approximately half a ton and needed 12 men to carry it.