A Walk through Time History of timekeeping from ancient to modern times. (at NIST)    Calendars through the Ages Systems of counting the days, months, and years. (at webexhibits.org)    Daylight Saving Time When and why do we change our clocks? (at webexhibits.org)    ClockWorks Illustrated mechanisms of many historical clocks. (at Britannica)    It's About Time Advances in timekeeping accuracy and atomic clocks. (at University of Wisconsin)    The Quartz Watch What's inside your wristwatch? See stories and timeline. (at Smithsonian) Disclaimer Note: Linking to these sites does not imply recommendation or endorsement of the information or commercial products by NIST or USNO.