During the Everest surveys they used prayor beads to keep count of paces and were aparently very accurate in their stride length..
"Because of this the survey of India, which had the task of providing the government with maps of the entire sub-continent and surrounding regions, found itself greatly hampered when it came to mapping northern Afghanistan, Turkestan and Tibet.
Then a young officer working for the Survey, Captain Thomas Montgomerie of the Royal Engineers, hit upon a brilliant solution. Why not, he asked his superiors, send native explorers trained in secret surveying techniques into these forbidden regions? They were far less likely to be detected than Europeans, however good the latter's disguise. If they were unfortunate enough to be discovered, moreover, it would be less politically embarrassing to the authorities than if a British officer was caught red-handed making maps in these highly sensitive and dangerous parts.
Surprisingly perhaps, in view of the British and Indian governments' determination not to become entangled in Central Asia, Montgomerie's bold plan was approved, and over the next few years a number of Indian explorers, including Mirza Shuja, were dispatched in great secrecy across the frontier. All of them hillmen, carefully chosen for their exceptional intelligence and resourcefulness. Because discovery, or even suspicion, would have spelt instant death, their existence and activities had to be kept as secret as possible. Even within the Survey of India they were known merely by a number or cryptonym. They were trained personally by Montgomery at Dehra Dun, the survey's headquarters in the Himalayan foothills. Some of the techniques and equipment he devised were extremely ingenious.
Montgomery first trained his men, through exhaustive practice to take a pace of known length which would remain constant whether they walked uphill, downhill or on the level. Next he taught them ways of keeping precise but discreet count of the number of such paces taken during a day's march. This enabled them to measure immense distances with remarkable accuracy and without arousing suspicion. Often they travelled as Buddhist pilgrims, many of whom regularly crossed the passes to visit holy sites of the ancient Silk Road. Every Buddhist carried a rosary of 108 beads on which to count his prayers, and also a small wood and metal prayer-wheel which he spun as he walked. Both of these Montgomerie turned to his advantage. From the former he removed eight beads, not enough to be noticed, but leaving a mathematically convenient 100. At every hundredth pace the pundit would automatically slip one bead. Each complete circuit of the rosary thus represented 10,000 paces.
The total for the days march, together with many other discreet observations, had somehow to be logged somewhere safe from prying eyes. It was here that the prayer-wheel, with its copper cylinder, proved invaluable. For concealed in this, in place of the usual hand written scroll of prayers, was a roll of blank paper. This served as a log-boo, which could easilly be got at by removing the top of the cylinder, and some of which are still preserved in the Indian State Archives. Then there was the problem of a compass, for the pundit was required to take regular bearings as he journeyed. Montgomerie decided to conceal this in the lid of the prayer-wheel. Thermometers, which were needed for calculating altitudes, were hidden in the tops of the pilgrims' staves. Mercury, essential for setting an artificial horizon when taking sextant readings, was hidden in cowrie shells and poured into a pilgrims begging bowl when required. Concealed pockets were added to the Pundits' clothing, and false bottoms, in which sextants could be hidden, were built into the chests which most native travellers carried. All this work was carried out in the Survey of India's workshops at Dehra Dun under Montgomerie's supervision."
