In the "Almagest" Ptolemy describes a meridian circle which consisted of a fixed graduated outer ring and a movable inner ring with sights that was mounted vertically and aligned with the meridian.
In the "Almagest" Ptolemy describes a meridian circle which consisted of a fixed graduated outer ring and a movable inner ring with tabs that used a shadow to set the Sun's position. It was mounted vertically and aligned with the meridian.