NIST TIME AND FREQUENCY BULLETIN 

NIST IR 6656-05 

No. 617 May 2009

 

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

 

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

 

3. PHASE DEVIATIONS FOR WWVB AND LORAN-C ............................................................................... 4 

 

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

 PHASE PERTURBATIONS ..................................................................................................................... 5 

5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS ........................................................... 5 

6. BIBLIOGRAPHY ....................................................................................................................................... 5 

 

This bulletin is published monthly. Address correspondence to: 

 

Eyvon M. Petty, Editor 

Time and Frequency Division 

National Institute of Standards and Technology 

325 Broadway 

Boulder, CO 8O3O5-3328 

(3O3) 497-3295 

Email: pettye@boulder.nist.gov

U.S. DEPARTMENT OF COMMERCE, GARY LOCKE, Secretary

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Patrick D. Gallagher, Deputy Director 

 

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2 

1. GENERAL BACKGROUND INFORMATION 

_______________________________________________________________________________________________________ 

ACRONYMS AND ABBREVIATIONS USED IN THIS BULLETIN

ACTS - Automated Computer Time Service 

BIPM - Bureau International des Poids et Mesures 

CS - Cesium Standard 

GPS - Global Positioning System 

IERS - International Earth Rotation Service 

LORAN - Long Range Navigation 

MC - Master Clock 

MJD - Modified Julian Date 

NIST - National Institute of Standards and Technology 

NOAA - National Oceanic and Atmospheric Administration 

NVLAP - National Voluntary Laboratory Accreditation Program 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 

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 2009 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

2 54923 324 ms 5 ns 

9 54930 314 ms 8 ns 

16 54937 307 ms 8 ns 

23 54944 297 ms 8 ns 

30 54951 288 ms 9 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: A positive leap second was added at the end of December 2008. 

 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 

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

1998, and 2005. 

 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 12 March 2009 

 -0.6 s beginning 0000 UTC 20 November 2008 

 -0.5 s beginning 0000 UTC 07 August 2008 

DUT1 = UT1 - UTC = -0.4 s beginning 0000 UTC 13 March 2008 

 -0.3 s beginning 0000 UTC 29 November 2007 
3 

 

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 10-day intervals. Five-day interval data are available in Circular T. 

0000 Hours Coordinated Universal Time

DATE MJD UTC-UTC(NIST) ns 

Mar. 28, 2009 54919 7.5 

Mar. 18, 2009 54909 7.1 

Mar. 08, 2009 54899 4.9 

Feb. 27, 2009 54889 4.3 

Feb. 17. 2009 54879 2.0 

Feb. 07, 2009 54869 1.7 

Jan. 28, 2009 54859 3.9 

Jan. 18, 2009 54849 3.9 

Jan. 08, 2009 54839 4.0 

Dec. 29, 2008 54829 4.1 

Dec. 19, 2008 54819 2.5 

Dec. 09, 2008 54809 0.7 

Nov. 29, 2008 54799 0.5 

Nov. 19, 2008 54789 -1.0 

Nov. 09, 2008 54779 -2.1 

Oct. 30, 2008 54769 -3.3 

Oct. 20, 2008 54759 -5.7 

Oct. 10, 2008 54749 -5.4 

Sep. 30, 2008 54739 -4.7 

Sep, 20, 2008 54729 -2.0 

Sep. 10, 2008 54719 -1.2 

Aug. 31, 2008 54709 -1.4 

Aug. 21, 2008 54699 0.9 

Aug. 11, 2008 54689 1.3 

Aug. 01, 2008 54679 3.0 

Jul. 22, 2008 54669 3.5 

Jul. 12, 2008 54659 4.1 

Jul. 02, 2008 54649 3.9 

 
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3. PHASE DEVIATIONS FOR WWVB AND LORAN-C

WWVB - The values shown for WWVB are the time differences between the time markers of the UTC(NIST) time scale 

and the first positive-going zero voltage crossover measured at the transmitting antenna. The uncertainty of 

the individual measurements is ±0.5 μs. The values listed are for 1300 UTC. 

LORAN-C - The values shown for LORAN-C represent the daily accumulated phase shift. The phase shift is measured by 

comparing the output of a LORAN receiver to the UTC(NIST) time scale for a period of 24 h. If data were not 

recorded on a particular day, the symbol (-) is printed. The stations monitored are Baudette, Minnesota (8970) 

and Boise City, Oklahoma (9610). The monitoring is done from the NIST laboratories in Boulder, Colorado. 

Note: The values shown for LORAN-C are in nanoseconds. 

UTC(NIST)-WWVB 

(60 kHz) UTC(NIST) - LORAN PHASE (ns)

ANTENNA PHASE 

LORAN-C 

(BAUDETTE) 

LORAN-C 

(BOISE CITY) 

DATE MJD (μs) (8970) (9610) 

04/01/2009 54922 5. 65 -43 -7 

04/02/2009 54923 5. 65 +11 +17 

04/03/2009 54924 5. 65 -10 -11 

04/04/2009 54925 5. 65 +42 -65 

04/05/2009 54926 5. 65 +48 +16 

04/06/2009 54927 5. 65 -74 +8 

04/07/2009 54928 5. 65 -4 -8 

04/08/2009 54929 5. 65 -69 +7 

04/09/2009 54930 5. 65 -60 -2 

04/10/2009 54931 5. 65 +31 0 

04/11/2009 54932 5. 65 -33 -24 

04/12/2009 54933 5. 65 +58 -50 

04/13/2009 54934 5. 65 +23 +37 

04/14/2009 54935 5. 65 -47 -7 

04/15/2009 54936 5. 65 +9 +15 

04/16/2009 54937 5. 65 -85 -26 

04/17/2009 54938 5. 65 +28 -24 

04/18/2009 54939 5. 65 +45 +2 

04/19/2009 54940 5. 65 -19 +14 

04/20/2009 54941 5. 65 +23 +32 

04/21/2009 54942 5. 65 -20 -6 

04/22/2009 54943 5. 65 -18 -4 

04/23/2009 54944 5. 65 -78 +6 

04/24/2009 54945 5. 65 -29 -6 

04/25/2009 54946 5. 65 +10 -16 

04/26/2009 54947 5. 65 -5 +16 

04/27/2009 54948 5. 65 +54 -1 

04/28/2009 54949 5. 65 -51 -11 

04/29/2009 54950 5. 65 +56 +9 

04/30/2009 54951 5. 65 0 -1 
 5 

 

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS 

OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS 

2 ms 

Station Apr 

2009 

 MJD Began 

UTC 

Ended 

UTC 

Freq. Feb 

2009 

MJD Began 

 UTC 

End 

UTC 

WWVB 04-29-09 54950 0056 0148 60 kHz

WWV 

WWVH 

5. 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. NIST-F1, a 

cold-atom cesium fountain frequency standard, has served as the U.S. primary time and frequency standard since 1999. The 

uncertainty of NIST-F1 is currently about 5 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. 

 

6. BIBLIOGRAPHY 

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). 
 6 

Table 7.1 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 Day, 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. 

Table 7.1 

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

Month xls

(s) 

x 

(ns) 

y 

(ns/d) 

 T0

(MJD) 

Valid until 0000 on: 

(MJD) 

 Jun 09 -34 -335212.0 -38.2* 54983 55013

 May 09 -34 -334027.8 -38.2 54952 54983*

 Apr 09 -34 -333225.6 -38.2 54931 54952

 Apr 09 -34 -332880.9 -38.3 54922 54931†

 Mar 09 -34 -331693.6 -38.3 54891 54922

 Feb 09 -34 -330621.2 -38.3 54863 54891

 Jan 09 -34 -329931.8 -38.3 54845 54863

 Jan 09 -34 -329432.6 -38.4 54832 54845†

 Dec 08 -33 -328895.0 -38.4 54818 54832

 Dec 08 -33 -328240.5 -38.5 54801 54818†

 Nov 08 -33 -327085.5 -38.5 54771 54801

 Oct 08 -33 -326392.5 -38.5 54753 54771

 Oct 08 -33 -325894.6 -38.3* 54740 54753†

 Sep 08 -33 -324745.6 -38.3 54710 54740

 Aug 08 -33 -323558.3 -38.3 54679 54710

 Jul 08 -33 -322792.3 -38.3 54659 54679

 Jul 08 -33 -322369.9 -38.4 54648 54659†

 Jun 08 -33 -321211.9 -38.6 54618 54648

 May 08 -33 -320594.3 -38.6 54602 54618

 May 08 -33 -320018.3 -38.4 54587 54602†

 Apr 08 -33 -319288.7 -38.4 54568 54587

 Apr 08 -33 -318867.4 -38.3 54557 54568†

† Rate change in mid-month 

*Provisional value