This arrangement makes a physical analog of just one trigonometrical term. Astronomy, time-keeping and geography provided other motivations for geometrical and trigonometrical research. Some are equivalent to standard trigonometrical formulae with the variables expressed as quadrance and spread. The triangulation survey was officially given the name of Great Trigonometrical Survey only in 1818. In 1832 he was posted to the Great Trigonometrical Survey under George Everest. Many trigonometrical stations were placed on hilltops around Hong Kong. In 1811 appeared the third volume of the "Trigonometrical Survey", by Mudge and Colby. Thirty parallel lines were drawn inside the quadrant, and trigonometrical calculations were done graphically. Trigonometrical stations are grouped together to form a network of triangulation. At its summit are a trigonometrical point and a radio mast.