In 1856, Andrew Waugh announced Everest (then known as Peak XV) as 29,002 ft (8,840 m) high, after several years of calculations based on observations made by the Great Trigonometric Survey.
The elevation of 8,848 m (29,029 ft) was first determined by an Indian survey in 1955, made closer to the mountain, also usingtheodolites. It was subsequently reaffirmed by a 1975 Chinese measurement 8,848.13 m (29,029.30 ft). In both cases the snow cap, not the rock head, was measured. In May 1999 an American Everest Expedition, directed by Bradford Washburn, anchored a GPS unit into the highest bedrock. A rock head elevation of 8,850 m (29,035 ft), and a snow/ice elevation 1 m (3 ft) higher, were obtained via this device. Although it has not been officially recognized by Nepal, this figure is widely quoted. Geoiduncertainty casts doubt upon the accuracy claimed by both the 1999 and 2005 surveys.
A detailed photogrammetric map (at a scale of 1:50,000) of the Khumbu region, including the south side of Mount Everest, was made by Erwin Schneider as part of the 1955 International Himalayan Expedition, which also attempted Lhotse. An even more detailed topographicmap of the Everest area was made in the late 1980s under the direction of Bradford Washburn, using extensive aerial photography.
It is thought that the plate tectonics of the area are adding to the height and moving the summit northeastwards. Two accounts suggest the rates of change are 4 mm (0.16 in) per year (upwards) and 3 to 6 mm (0.12 to 0.24 in) per year (northeastwards), but another account mentions more lateral movement (27 mm/1.1 in), and even shrinkage has been suggested
