The Great Trigonometrical Survey began in 1802 and ran for most of the century, working north from the southern tip of India by measuring the angles of chains of triangles. The theodolites weighed half a tonne and took a dozen men to carry. Among its results was the first calculated height for the world’s highest peak, computed in the survey office in 1852.
Why this oneThe survey took longer than most of the wars fought over the same ground.