Pundit Nain Singh: AlgoMantrics In History

Nain Singh walked twelve hundred miles in the employ of the British Secret Service. Dressed as a pilgrim, he was dispatched to survey the road to Lhasa. Singh was specially trained to walk every pace at exactly 33 inches. His pilgrim's rosary, on which he counted several million of those paces, was used to click off the distances. The rosary had only one hundred beads on it, instead of the sacred 108, and if any of the numerous guards, police, and customs officials had bothered to count he would have been instantly killed.
Singh's pilgrim outfit had a few other special modifications. His tea bowl was used to hold mercury to find the horizon. His walking stick held a thermometer, which he would dip into the tea water just as it came to a boil and thus determine the altitude.

The biggest sacrilege, though, was Nain Singh's prayer wheel. A prayer wheel is a holy object containing the Tibetan mantra "Om! Mane Padme Hum!" ("Hail! Jewel in the Lotus!") written many times on a scroll of paper. The scroll is put inside the wheel, and when it is spun the prayers are sent upwards. In Lhasa, and later in Dharamsala, huge prayer wheels will contain a million prayers, all sent with a spin of the mighty discs.

Inside Singh's prayer wheel was his route survey, careful notes that showed the altitudes, the landmarks, and the distances that he walked. The route survey was brought back to Dehra Dun where Captain T. G. Montgomerie, the man who hired Nain Singh, was building a map.

[LINK] Wikipedia
[LINK] Image of Nain Singh's Compass