Worldwide time change dates. An overview of the ISO 8601 notation for dates. In History Today in history every day - often with pictures and sound. The Calendar Summarizes the history of various calendars developed and used over the centuries. Atomic Clock Time Displayed in a variety of useful formats.
Site is a front-end to U.S. government atomic clocks.
The National Institute of Standards and Technology maintains time and frequency standards for the United States. Calendar Studies Information about calendar history and calendar reform. Data A directory of sites providing descriptions of civil timekeeping concepts, source code, databases, and maps. English Calendar Includes an ecclesiastical calendar and a section on old and new style dating. Information on all things relating to calendars, dates, holidays, and time.