> A maser ensemble time scale is just sufficiently stable and accurate to take advantage of the performance of intermittently operating primary frequency standards such as NIST-F1 and F2.
Devices like F1 are used to correct hydrogen masers which are extremely stable but have systemic errors in frequency. Unlike the masers, they don't run all the time, or (or last I saw-- anywhere close to most of the time, though I'm not quickly finding a link with operating stats).
Thanks, it looks like you're right. Exchanges care about UTC(NIST), which is calibrated using a variety of clocks. NIST-F1 is specifically run and calibrated for a few weeks a couple times a year, which is intermittent.
UTC(NIST) is the coordinated universal time scale maintained at NIST. The UTC(NIST) time scale comprises an ensemble of cesium beam and hydrogen maser atomic clocks, which are regularly calibrated by the NIST primary frequency standard. The number of clocks in the time scale varies, but is typically around ten. The outputs of the clocks are combined into a single signal by using a weighted average. The most stable clocks are assigned the most weight. The clocks in the UTC(NIST) time scale also contribute to the International Atomic Time (TAI) and Coordinated Universal Time (UTC).
UTC(NIST) serves as a national standard for frequency, time interval, and time-of-day. It is distributed through the NIST time and frequency services and continuously compared to the time and frequency standards located around the world.
