In order to calculate the height of Mount Everest, classical topographical techniques were initially applied. First a baseline of several kilometers was measured, along a terrain whose altitude above sea level was known.
The top of the mountain could be seen from both ends of the line and a theodolite -a precision instrument- was used to determine the angles formed with respect to the base line.
Knowing two angles and the length of one side of a triangle the other sides can be calculated and, with later calculations, the height. Surveyors measured Everest from six locations, and obtained different figures ranging from 8,836 to 8,847 meters. The average was 8,839 m, but it was finally agreed to be 8,840 m.
The hierarchy of Everest as the highest mountain in the world was unquestionable until 1986, when George Wallerstein, of the University of Washington, applying a different method proclaimed that another Himalayan mountain, the K-2 could be 11 meters higher.
Wellerstein's assertion was so astonishing that in 1987 an Italian expedition decided to prove it. Researchers placed receivers on Everest and Mount K-2, and used a system of signals to establish their exact height and position. This was decisive since the discrepancies in the height of the mountains are due to errors in the altitude of the baseline from which the calculations are made.
The group, led by geologist Ardito Desio, calculated the altitude of the two summits with theodolites located where the receivers had been placed. His conclusion was that Wellerstein was wrong: Everest turned out to be 8,872 m: 256 more than K-2.
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