The Sextant in its earliest known form consisted of divided circles and compasses with simply sights. An early Creek astronomer of the second century after Christ, Claudius Ptolemaeus, or more commonly called Ptolemy, wrote a book entitled Megale Syntaxis tes Astron- omias, also known by the Arabic title Almagest. The instrument described in this book was called the Astrolable and was used to measure the angular distance between stars. It was made of two concentric vertical circles, the largest and outer circle was about sixteen inches in diameter with graduated arc; the central ring was movable and carried the two sights.