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Commonly used units

Units commonly used for Earth orientation:
1 mas = 1 milliarcsecond = 1 thousandth of a second of arc (for polar motion & nutation);
1 ms = 1 millisecond = 1 thousandth of a second of time (for UT1);
1 mas equals an equatorial shift at the Earth's surface of 3.1 cm;
1 ms equals the time it takes for the Earth to spin 15 mas (46.5 cm at the equator)

USNO Master Clock Time
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