Variations on this instrument (above) have been around since the mid-1500s, according to the Smithsonian National Museum of American History. It’s basically a rotating telescope mounted on a tripod that allows a user to measure the angles between two points. Early attempts to measure Everest in the 1800s used theodolites such as the half-ton instrument pictured above, requiring surveyors to lug heavy gear as they zig-zagged their way north from the Bay of Bengal, Freddie Wilkinsonreports for Nat Geo. Until this week, the official height recognized by the government of Nepal was 29,028 feet above sea level—a number calculated in 1954 using a similar method.



To get the new height of 29,031.69 feet above sea