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. Author manuscript; available in PMC: 2020 Oct 22.
Published in final edited form as: Phys Rev Appl. 2019;12(4):https://doi.org/10.1103/physrevapplied.12.044069.

FIG. 3.

FIG. 3.

(a) Shows the fractional frequency difference between the Yb clock and AT1 during MJD 58054–58214. Note AT1, composed of a few hydrogen masers and a few commercial cesium clocks, is a free-running microwave time scale at NIST. (b) Shows the time difference between AT1′ and UTC (red dots) during MJD 58054–58214. AT1′ is the NIST time scale that is steered to the Yb clock. AT1′ is set to 0 ns initially. AT1′ has a root-mean-square variation of 0.4 ns with respect to UTC during MJD 58054–58214. The time difference between AT1 and UTC (blue dots) is shown for reference. A constant frequency offset of +4.278 × 10−13 (measured from the first two points on the plot) in AT1 has already been removed. (c),(d) Show the behavior of AT1′ and AT1 during MJD 58215–58300. During MJD 58215–58240 (gray region), the Yb clock ceases regular operation. After Yb-clock data resumes on MJD 58241, AT1′ becomes flat with respect to UTC [black dashed line in (d)] indicating prompt frequency recalibration. The frequency change of AT1 is illustrated by the black arrows.