The master clock to which time and frequency measurements for the U. S. Department of Defense are referenced, i.e., are traceable. Note 1: The U. S. Naval Observatory master clock is designated as the DOD Master Clock. Note 2: The U. S. Naval Observatory master clock is one of the two standard time and frequency references for the U. S. Government in accordance with Federal Standard 1002-A. The other standard time and frequency reference for the U. S. Government is the National Institute of Standards and Technology (NIST) master clock.