The Equation of Time AEquatio Dierum

The Equation-of-Time denotes the variance between Mean Time as told by the Stars and Solar Time as told by the Sun. It was initially identified by Ptolemy around 200 CE. During the Early Middle Ages, astronomers utilized this Equation to assist in lunar observations. Throughout the High & Late Middle Ages, sundials held prominence as the primary means of timekeeping, indicating Solar Time. However, in the 17th century CE, the emergence of precise pendulum clocks and watches prompted a gradual shift towards the adoption of Mean Time over Solar Time. In particular, the use of Solar Time corrected by the Equation-of-Time to determine local mean time, was used in the determination of longitude at sea. Prior to the availability of time signals, sundials - together with tables detailing the Equation - were used to set clocks.