Assertion: physicist's time | /r/HasProperty | nist-f1
Facets:
value: currently
type: TEMPORAL
value: to nist-7
type: LOCATION
Source sentences:
text: The primary time standard in the U.S. is currently NIST-F1, a laser-cooled Cs fountain, the latest in a series of time and frequency standards, from the ammonia-based atomic clock (1949) to the caesium-based NBS-1 (1952) to NIST-7 (1993).