A theodolite is the instrument a land surveyor stands behind — a small telescope mounted on a tripod, sitting in a frame that lets it turn two ways: side to side (horizontal angle) and up and down (vertical angle). Both movements are read off finely marked circles, so the surveyor can say exactly how many degrees apart two distant points are. That is all it does: it measures angles, very precisely. It does not measure distance by itself — old surveying got distance from angles plus mathematics, or from a measuring chain, and modern machines add a laser for that. This is why you see one before a building goes up, a road is cut, or a boundary between two pieces of land is settled. The word is a technical one; ordinary people rarely say it, and many who have seen the machine by the roadside do not know its name. Today most working surveyors use an electronic version called a 'total station' (a theodolite plus a distance meter plus a computer), and some of them will still call the whole thing a theodolite out of habit — so if a modern surveyor says 'theodolite', they may mean the newer machine. Note that it is always a countable object: a theodolite, two theodolites.

經緯儀（測量土地用的角度測量儀器）。注意台灣工地和測量現場更常聽到的是「全站儀」（total station），那是加了電子測距功能的新式機型，但老一輩仍習慣通稱經緯儀。