The tetrantas (Quadrant) of Hipparhos (2nd c. B.C.)

(the first latitude locator of daily use)

It was a measuring instrument which was used in astronomy and navigation for the calculation of astronomical sizes and in topography and in construction for the measurement of terrestrial distances (e.g. the height of a building). It consisted of graduated in degrees quadrant which had an aiming device at one edge and from its centre hung a plumb bob. The latitude of each place could be found directly by aiming the Pole Star (it was equivalent to the complement angle of the angle that was shaped by the aiming line with the thread) and indirectly by the measurement of the zenith of some other celestial body (e.g. the Sun). Later on straight lined scales were engraved on the surface of the instrument for the conversion of the terrestrial angles in the proportions of lengths but also monthly arcs with curved hour lines for one or more latitudes. A moving button was also added which slid at length of the thread and was regulated depending on the month which was indicated by the zodiac at the other edge of the instrument. The instrument could be used as a position locator at any given hour of the day, while with any given latitude as a sundial. The level astrolabes constitute its evolution.