The Gregorian calendar was a system for measuring one solar year on Earth. It was devised as an improvement upon the Julian calendar, and was used as a standard by Humans throughout the planet's Western hemisphere from 15 October 1582 until the adoption of stardates, although conversion from stardates to Earth year dating was common in practice. (ST novel: Excelsior: Forged in Fire) The first chapter of Watching the Clock presented dates identified as Gregorian calendar reckoning. Subsequent chapters were dated using other calendars from various worlds.