Question: A unit of time or time unit is any particular time interval, used as a standard way of measuring or expressing duration, the exact modern definition, is from the National Institute of Standards and Technology (NIST), a measurement standards laboratory, and a non-regulatory agency of which organization?
Sentence (from "Unit of time"): The base unit of time in the International System of Units (SI), and by extension most of the Western world, is the second, defined as about 9 billion oscillations of the caesium atom.
Relevant evidence: No