sekhterion
The sekhterion, also known as a sector square or sectorial, is an ancient Greek surveying instrument used primarily for measuring angles and establishing right angles in land division and construction. Dating back to at least the 4th century BCE, it was a key tool in the field of geodesy, the science of measuring and mapping the Earth’s surface.
The sekhterion consisted of a square or rectangular base with a rotating arm attached at one corner.
While the sekhterion shared similarities with other ancient surveying tools like the groma (used in Roman times),
Over time, the sekhterion was largely replaced by more advanced instruments, such as the astrolabe and theodolite,