In the 1860s, Thomas George Montgomerie, a captain in the survey, realised that the solution to this problem would be to train natives from Indian border states such as Sikkim to be surveyors, and have them explore the region.
[1] A prayer wheel did not hold the common Buddhist mantra Om mani padme hum, instead, "the scroll hidden within (...) was replaced by a blank roll of paper upon which data could be surreptitiously recorded.
"[6] Pundit Nain Singh Rawat also found that these could be used to ward off curious co-travelers: each time someone came too near, he would start whirling the wheel around and pretend to be in religious contemplation.
The pundits were given extensive training in basic surveying: they learned to use the sextant, determine height by measuring the temperature of boiling water, and make astronomical observations.
Through their exploration efforts, they managed to bring back vital data that allowed the mapping of areas lying north of India (which were forbidden to Europeans, such as Tibet) with remarkable precision.