Early records show that without doubt the first mechanical instrument used for measuring angles, particularly in connection with navigation, was the astrolabe. There seems to be a slight difference of opinion among early authors as to who should have the credit for making the first instrument but it seems to be agreed that it was used by the early Greek and Arab astronomers and navigators. Several authors give the credit to Hipparchus in about 150 B.C., while others mention that it was invented by Apollonius, a philosopher of Perga in 240 B.C. This instrument in its simplest form consisted of a circle with sighting bar or radial pointer fitted with sight vanes on each end. It was suspended in a vertical position from a ring on top, sights were taken of two stars, or of a star and the horizon and the angle computed from the graduations on the outer edge of the circle.
Type used during the sixteenth century. Made of brass plate elaborately decorated. Outer edge is graduated, has sighting bar with sight vane on each end of bar.