URLs listed in this category:
A Walk through Time
Presentation of the Physics Laboratory of the National Institutes of Standards and Technology on the evolution of time measurement.
http://physics.nist.gov/GenInt/Time/time.html
Atomic Clock Time
Provides atomic clock information and resources.
http://www.atomictime.net/
Hermetic System: Calendar Studies
Contains presentations on the different calendar systems, types, and date formats.
http://www.hermetic.ch/cal_stud.htm