Where does my computer get the time from?

A talk on where computers get their time traces the chain from NTP servers to GPS receivers, then to the US Naval Observatory (USNO) and its atomic clocks. The USNO receives Earth-rotation information from the IERS in Paris, and the BIPM in Paris maintains UTC from national timing laboratories' measurements. The article also covers how the caesium second's definition was calibrated in 1955–1958 by Louis Essen and Jack Parry with help from William Markowitz of the USNO, who measured the "ephemeris second."