NISTIR 7980-05 

NIST Time and Frequency Bulletin 

Petrina C. Potts, Editor 

http://dx.doi.org/10.6028/NIST.IR.7980-05 
 

NISTIR 7980-04 

NIST Time and Frequency Bulletin 

Petrina C. Potts, Editor 

Time and Frequency Division 

Physical Measurement Laboratory 

http://dx.doi.org/10.6028/NIST.IR.7980-05 

May 2014 

U.S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director 
 

 

 

 

 

 

 

NIST TIME AND FREQUENCY BULLETIN 

NIST IR 7980-05 

No. 677 April 2014
 

1. GENERAL BACKGROUND INFORMATION........................................................................................... 2 

2. TIME SCALE INFORMATION ............................................................................................................... 2 

3. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

 PHASE PERTURBATIONS ..................................................................................................................... 4 

4. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS ........................................................... 4 

5. UTC(NIST) – AT1 PARAMETERS ........................................................................................................... 5 

This bulletin is published monthly. Address correspondence to: 

Petrina C. Potts, Editor 

Time and Frequency Division 

National Institute of Standards and Technology 

325 Broadway 

Boulder, CO 8O3O5-3328 

(3O3) 497-3295 

Email: ppotts@boulder.nist.gov
 

U.S. DEPARTMENT OF COMMERCE, Penny Pritzker, Secretary 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Patrick D. Gallagher, Under Secretary of Commerce 

for Standards and Technology and Director 

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1. GENERAL BACKGROUND INFORMATION 

ACRONYMS AND ABBREVIATIONS USED IN THIS BULLETIN 

ACTS - Automated Computer Time Service 

BIPM - Bureau International des Poids et Mesures 

GPS - Global Positioning System 

IERS - International Earth Rotation Service 

MC - Master Clock 

MJD - Modified Julian Date 

NIST - National Institute of Standards and Technology ns - nanosecond 

SI - International System of Units μs - microsecond 

TA - Atomic Time ms - millisecond 

TAI - International Atomic Time s - second 

USNO - United States Naval Observatory min - minute 

UT1 - Universal Time (Astronomical) 

UTC - Coordinated Universal Time 

2. TIME SCALE INFORMATION 

 The values listed below are based on data from the IERS, the USNO, and NIST. The UTC(USNO,MC) - UTC(NIST) values are 

averaged measurements from all available common-view GPS satellites (see bibliography on page 5). UTC - UTC(NIST) data are 

on page 3. 

 0000 HOURS COORDINATED UNIVERSAL TIME 

APR 2014 MJD UT1-UTC(NIST) 

(±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

(±20 ns) 

3 

10 

17 

24 

56750 

56757 

56764 

56771 

-207 ms 

-216 ms 

-225 ms 

-235 ms 

+6 ns 

+6 ns 

+5 ns 

+3 ns 

The master clock pulses used by the WWV, WWVH, and WWVB time-code transmissions are referenced to the UTC(NIST) time 

scale. Occasionally, 1 s is added to the UTC time scale. This second is called a leap second. Its purpose is to keep the UTC time 

scale within ±0.9 s of the UT1 astronomical time scale, which changes slightly due to variations in the Earth’s period of rotation. 

NOTE: No leap second will be added at the end of June 2014. 

Positive leap seconds, beginning at 23 h 59 min 60 s UTC and ending at 0 h 0 min 0 s UTC, were inserted in the UTC time 

scale on 30 June 1972, 1981-1983, 1985, 1992-1994, 1997, and 2012, and on 31 December 1972-1979, 1987, 1989, 1990,1995, 

1998, 2005, and 2008. 

The use of leap seconds ensures that UT1 - UTC will always be held within ±0.9 s. The current value of UT1 - UTC is called the 

DUT1 correction. DUT1 corrections are broadcast by WWV, WWVH, WWVB, and ACTS and are printed below. These corrections 

may be added to received UTC time signals in order to obtain UT1. 

 -0.3 s beginning 0000 UTC 08 May 2014 

- 0.2 s beginning 0000 UTC 20 February 2014 

- 0.1 s beginning 0000 UTC 21 November 2013 

 +0.0 s beginning 0000 UTC 22 August 2013 

 +0.1 s beginning 0000 UTC 11 April 2013 

 +0.2 s beginning 0000 UTC 31 January 2013 

 +0.3 s beginning 0000 UTC 25 October 2012 

 +0.4 s beginning 0000 UTC 01 July 2012 

DUT1 = UT1 - UTC = - 0.6 s beginning 0000 UTC 10 May 2012 

- 0.5 s beginning 0000 UTC 09 February 2012 

- 0.4 s beginning 0000 UTC 04 November 2011 

- 0.3 s beginning 0000 UTC 12 May 2011 

- 0.2 s beginning 0000 UTC 06 January 2011 

- 0.1 s beginning 0000 UTC 03 June 2010 

 +0.0 s beginning 0000 UTC 11 March 2010 

 +0.1 s beginning 0000 UTC 12 November 2009 

 +0.2 s beginning 0000 UTC 11 June 2009 

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The difference between UTC(NIST) and UTC has been within ±100 ns since July 6, 1994. The table below shows values

of UTC ‐ UTC(NIST) as supplied by the BIPM in their Circular T publication for the most recent 310‐day period in which

data are available. Data are given at ten‐day intervals. Five‐day interval data are available inCircular T .

0000 Hours Coordinated Universal Time

DATE MJD UTC‐UTC(NIST), ns

Mar 23, 2014 56739 5.8

Mar. 13, 2014 56729 6.3

Mar. 03, 2014 56719 5.7

Feb. 21, 2014 56709 5.1

Feb. 11, 2014 56699 4.3

Feb. 1, 2014 56689 3.2

Jan. 22, 2014 56679 2.1

Jan. 12, 2014 56669 0.6

Jan. 2, 2014 56659 ‐0.7

Dec. 23, 2013 56649 ‐2.6

Dec. 13, 2013 56639 ‐4.6

Dec. 3, 2013 56629 ‐5.1

Nov. 23. 2013 56619 ‐5.9

Nov. 13, 2013 56609 ‐4.8

Nov. 3, 2013 56599 ‐2.8

Oct. 24, 2013 56589 1.1

Oct. 14, 2013 56579 3.8

Oct. 4, 2013 56569 6.9

Sep. 24, 2013 56559 10.9

Sep. 14, 2013 56549 13.1

Sep. 4, 2013 56539 13.9

Aug. 25, 2013 56529 14.0

Aug. 15, 2013 56519 14.5

Aug. 5, 2013 56509 14.6

Jul. 26, 2013 56499 14.4

Jul. 16, 2013 56489 14.0

Jul. 6, 2013 56479 13.5

Jun. 26, 2013 56469 12.3

Jun. 16, 2013 56459 9.8

Jun. 6, 2013 56449 7.9

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3. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS 

OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS 

2 ms 

Station Apr 

2014 

MJD Began 

UTC 

Ended 

UTC 

Freq. Apr

2014 MJD Began

 UTC 

End 

UTC 

WWVB 

WWV 

WWVH 

4. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS 

 Primary frequency standards developed and operated by NIST are used to provide accuracy (rate) input to the BIPM and to provide 

the best possible realization of the SI second. NIST-F1, a cold-atom cesium fountain frequency standard, has served as the U.S. 

primary standard of time and frequency since 1999. The uncertainty of NIST-F1 is currently about 3 parts in 1016. 

The AT1 scale is run in real-time by use of data from an ensemble of cesium standards and hydrogen masers. It is a free-running 

scale whose frequency is maintained as nearly constant as possible by choosing the optimum weight for each clock that contributes 

to the computation. 

UTC(NIST) is generated as an offset from our real-time scale AT1. It is steered in frequency towards UTC by use of data published 

by the BIPM in its Circular T. Changes in the steering frequency will be made, if necessary, at 0000 UTC on the first day of the 

month, and occasionally at mid-month. A change in frequency is limited to no more than ±2 ns/day. The frequency of UTC(NIST) is 

kept as stable as possible at other times. 

UTC is generated at the BIPM by use of a post-processed time-scale algorithm and is not available in real-time. The parameters 

that we use to generate UTC(NIST) in real-time are therefore based on an extrapolation of UTC from the most recent available data. 

References: 

Allan, D.W.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm for an atomic time scale," Metrologia, Vol.11, No.3, pp. 133-138 

(1975). 

Allan, D.W.; Davis, D.D.; Weiss, M.A.; Clements, A.; Guinot, B.; Granveaud, M.; Dorenwendt, K.; Fischer, B.; Hetzel, P.; Aoki, S.; 

Fujimoto, M.; Charron, L.; and Ashby, N., “Accuracy of international time and frequency comparisons via global positioning system 

satellites in common-view,” IEEE Transactions on Instrumentation and Measurement, Vol. IM-34, pp.118-125 (1985). 

Heavner, T.P.; Jefferts, S.R.; Donley; E.A.; Shirley, J.H. and Parker, T.E., “NIST F1; recent improvements and accuracy evaluations,” 

Metrologia, Vol. 42, pp. 411-422 (2005). 

Jefferts, S.R.; Shirley, J.; Parker, T.E.; Heavner, T.P.; Meekhof, D.M.; Nelson, C., Levi, F.; Costanza, G.; De Marchi, A.; Drullinger, 

R.; Hollberg, L.; Lee, W.D.; and Walls, F.L., “Accuracy evaluation of NIST-F1,” Metrologia, Vol. 39, pp. 321-336 (2002). 

Lewandowski, W. and Thomas, C., “GPS Time transfer,” Proceedings of the IEEE, Vol. 79, pp. 991-1000 (1991). 

Parker, T.E.; Jefferts, S.R.; Heavner, T.P.; and Donley, E.A., “Operation of the NIST-F1 caesium fountain primary frequency standard 

with a maser ensemble, including the impact of frequency transfer noise,” Metrologia, Vol. 42, pp. 423-430 (2005). 

Weiss, M.A.; Allan, D.W., “An NBS Calibration Procedure for Providing Time and Frequency at a Remote Site by Weighting and 

Smoothing of GPS Common View Data,” IEEE Transactions on Instrumentation and Measurement, Vol. IM-36, pp. 572-578 (1987). 

4 
5. UTC(NIST) – AT1 PARAMETERS 

The table below lists parameters that are used to define UTC(NIST) with respect to our real-time scale AT1. To find the 

value of UTC(NIST) - AT1 at any time T (expressed as a Modified Julian Date, including a fraction if needed), the 

appropriate equation to use is the one for which the desired T is greater than or equal to the entry in the T0 column and 

less than the entry in the last column. The values of xls, x, and y for that month are then used in the equation below to 

find the desired value. The parameters x and y represent the offsets in time and frequency, respectively, between 

UTC(NIST) and AT1; the parameter xls is the number of leap seconds applied to both UTC(NIST) and UTC, as specified 

by the IERS. Leap seconds are not applied to AT1. 

UTC(NIST) - AT1 = xls + x + y*(T -T0)

Month xls 

(s) 

x 

(ns) 

y 

(ns/d)

 T0 

(MJD) 

Valid until 0000 on: 

(MJD) 

Jul 14 -35 -405942.5 -37.55* 56839 56870 

Jun 14 -35 -404816 -37.55 56809 56839* 

May 14 -35 -403651.9 -37.55 56778 56809 

Apr 14 -35 -402525.4 -37.55 56748 56778 

Mar 14 -35 -401624.2 -37.55 56724 56748 

Mar 14 -35 -401360.7 -37.65 56717 56724† 

Feb 14 -35 -400306.5 -37.65 56689 56717 

Jan 14 -35 -399136.3 -37.75 56658 56689 

Dec 13 -35 -397966.0 -37.75 56627 56658 

Nov 13 -35 -397664.0 -37.75 56619 56627 

Nov 13 -35 -396836.8 -37.6 56597 56619† 

Oct 13 -35 -395677.4 -37.4 56566 56597 

Sep 13 -35 -394929.4 -37.4 56546 56566 

Sep 13 -35 -394553.4 -37.6 56236 56546† 

Aug 13 -35 -393726.2 -37.6 56514 56536 

Aug 13 -35 -393386.0 -37.8 56505 56514† 

Jul 13 -35 -392554.4 -37.8 56483 56505 

Jul 13 -35 -392213.3 -37.9 56474 56483† 

Jun 13 -35 -391070.3 -38.1 56444 56474 

May 13 -35 -390689.3 -38.1 56434 56444 

May 13 -35 -389882.9 -38.4 56413 56434† 

Apr 13 -35 -388730.9 -38.4 56383 56413 

Mar 13 -35 -388308.5 -38.4 56372 56383 

Mar 13 -35 -387542.5 -38.3 56352 56372† 

† Rate change in mid-month 

*Provisional value 

5