NISTIR 1149-08 

NIST Time and Frequency Bulletin 

Petrina C. Potts, Editor 
 

NISTIR 1149-08 

NIST Time and Frequency Bulletin 

Petrina C. Potts, Editor 

Time and Frequency Division 

Physical Measurement Laboratory 

August 2013 

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 1149-08 

No. 668 August 2013
 

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 

JUL 2013 MJD UT1-UTC(NIST) 

(±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

(±20 ns) 

4 

11 

18 

25 

56477 

56484 

56491 

56498 

+57 ms 

+58 ms 

+56 ms 

+53 ms 

+18 ns 

+18 ns 

+18 ns 

+17 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 December 2013. 

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. 

DUT1 = UT1 - UTC = 

 +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 

- 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 

 +0.3 s beginning 0000 UTC 12 March 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

Jun. 26, 2913 56469 12.3

Jun. 16, 2013 56459 9.8

Jun. 6, 2013 56449 7.9

May 27, 2013 56439 6.4

May 17, 2013 56429 4.3

May 7, 2013 56419 ‐0.6

Apr. 27, 2013 56409 ‐4.8

Apr. 17, 2013 56399 ‐8.9

Apr. 7, 2013 56389 ‐11.9

Mar. 28, 2013 56379 ‐14.4

Mar. 18, 2013 56369 ‐16.5

Mar. 8, 2013 56359 ‐17.9

Feb. 26, 2013 56349 ‐18.5

Feb. 16, 2013 56339 ‐20.2

Feb. 6, 2013 56329 ‐19.0

Jan. 27, 2013 56319 ‐16.8

Jan. 17, 2013 56309 ‐14.8

Jan. 7, 2013 56299 ‐11.8

Dec. 28, 2012 56289 ‐9.5

Dec. 18, 2012 56279 ‐6.6

Dec. 8, 2012 56269 ‐4.7

Nov. 28, 2012 56259 ‐3.1

Nov. 18, 2012 56249 ‐1.3

Nov. 8, 2012 56239 ‐1.4

Oct. 29, 2012 56229 0.5

Oct. 19, 2012 56219 2.5

Oct. 9, 2012 56209 2.8

Sep. 29, 2012 56199 2.9

Sep. 19, 2012 56189 3.9

Sep. 9, 2012 56179 3.3

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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 Jul 

2013 

MJD Began 

UTC 

Ended 

UTC 

Freq. Jul 

2013 MJD Began

 UTC 

End 

UTC 

WWVB 07-20-13 

07-22-13 

56493 

56495 

2043 

1111 

2137 

1227 

60 kHz 

60 kHz 

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) 

Sep 13 -35 -394557.8 -37.8* 56236 56556 

Aug 13 -35 -393386.0 -37.8 56505 56536* 

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† 

Feb 13 -35 -387044.6 -38.3 56339 56352

 Feb 13 -35 -386474.6 -38.0 56324 56339† 

Jan 13 -35 -385828.6 -38.0 56307 56324 

Jan 13 -35 385300.8 -37.7 56293 56307† 

Dec 12 -35 -384132.1 -37.7 56262 56293 

Nov 12 -35 -383001.1 -37.7 56232 56262 

Oct 12 -35 -381832.4 -37.7 56201 56232 

Sep 12 -35 -380701.4 -37.7 56171 56201 

Aug 12 -35 -379532.7 -37.7 56140 56171 

Jul 12 -35 -3783640 -37.7 56109 56140 

Jun 12 -34 -377233 -37.7 56079 56109 

May 12 -34 -376705.2 -37.7 56065 56079 

May 12 -34 -376059.2 -38 56048 56065† 

† Rate change in mid-month 

*Provisional value 

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