Scaphion

The scaphion was a portable gnomon, developed by hellenistic astronomers. They put a gnomon in a metallic hemisphere, which was divided inside in concentric circles. They could use it for determination of geographical coordinates from measured solar altitudes. Using this measuring instrument Eratosthenes of Cyrene (ca. 220 BC) had measured the length of Earth's meridian, and after that they used this instrument to survey smaller regions as well.