NIST TIME AND FREQUENCY BULLETIN 

NIST IR 6639-05 

NO. 581 MAY 2006

 

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, CARLOS GUTIERREZ, Secretary

TECHNOLOGY ADMINISTRATION, Robert Cresanti, Under Secretary of Commerce for Technology 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, William A. Jeffrey, 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 

NVLAP - National Voluntary Laboratory Accreditation Program 

NIST - National Institute of Standards and Technology 

NOAA - National Oceanic and Atmospheric Administration 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 2006 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

6 53831 263 ms 15 ns 

13 53838 255 ms 18 ns 

20 53845 250 ms 19 ns 

27 53852 241 ms 18 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 rotation. 

 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, 1993, 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 24 October 2002 

 -0.4 s beginning 0000 UTC 03 April 2003 

 -0.5 s beginning 0000 UTC 29 April 2004 

DUT1 = UT1 - UTC = -0.6 s beginning 0000 UTC 17 March 2005 

+0.3 s beginning 0000 UTC 01 January 2006 

+0.2 s beginning 0000 UTC 27 April 2006 
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. 25, 2006 53819 5.7 

Mar. 15, 2006 53809 3.8 

Mar. 05, 2006 53799 3.2 

Feb. 23, 2006 53789 2.5 

Feb. 13, 2006 53779 1.3 

Feb. 03, 2006 53769 2.0 

Jan. 24, 2006 53759 2.0 

Jan. 14, 2006 53749 4.1 

Jan. 04, 2006 53739 4.1 

Dec. 25, 2005 53729 3.7 

Dec. 15, 2005 53719 2.6 

Dec. 05, 2005 53709 3.4 

Nov. 25, 2005 53699 0.1 

Nov. 15, 2005 53689 -4.3 

Nov. 05, 2005 53679 -7.2 

Oct. 26, 2005 53669 -9.7 

Oct. 16, 2005 53659 -11.5 

Oct. 06, 2005 53649 -12.2 

Sep. 26, 2005 53639 -12.7 

Sep. 16, 2005 53629 -12.6 

Sep. 06, 2005 53619 -11.8 

Aug. 27, 2005 53609 -11.6 

Aug. 17, 205 53599 -10.3 

Aug. 07, 2005 53589 -6.1 

Jul. 28, 2005 53579 -1.9 

Jul. 18, 2005 53569 4.3 

Jul. 08, 2005 53559 8.4 

Jun. 28, 2005 53549 10.5 

Jun. 18, 2005 53539 15.6 

Jun. 08, 2005 53529 14 

 
4 

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) 

04/01/06 53826 5. 65 +85 -12 

04/02/06 53827 5. 65 -40 +13 

04/03/06 53828 5. 65 +69 -15 

04/04/06 53829 5. 65 +17 -7 

04/05/06 53830 5. 65 -85 -3 

04/06/06 53831 5. 65 -51 +17 

04/07/06 53832 5. 65 +54 -3 

04/08/06 53833 5. 65 -46 +2 

04/09/06 53834 5. 65 -48 +17 

04/10/06 53835 5. 65 +24 -10 

04/11/06 53836 5. 65 -70 -3 

04/12/06 53837 5. 65 +38 -4 

04/13/06 53838 5. 65 +1 +11 

04/14/06 53839 5. 65 -52 -34 

04/15/06 53840 5. 65 +46 +1 

04/16/06 53841 5. 65 -6 +28 

04/17/06 53842 5. 65 +32 -20 

04/18/06 53843 5. 65 -76 -4 

04/19/06 53844 5. 65 -8 -5 

04/20/06 53845 5. 65 -10 -17 

04/21/06 53846 5. 65 +37 +21 

04/22/06 53847 5. 65 +35 -0 

04/23/06 53848 5. 65 -9 -27 

04/24/06 53849 5. 65 -49 +35 

04/25/06 53850 5. 65 +84 -6 

04/26/06 53851 5. 65 -51 -6 

04/27/06 53852 5. 65 +10 -13 

04/28/06 53853 5. 65 -20 +12 

04/29/06 53854 5. 65 +4 +20 

04/30/06 53855 5. 65 -17 -16 
5 

 

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS 

OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS 

2 ms 

Station APR 

2006 

 MJD Began 

UTC 

Ended 

UTC 

Freq. APR 

2006 

MJD Began 

 UTC 

End 

UTC 

WWVB 04/24/06 53849 1215 1232 60 kHz 

WWVB 04/10/06 53835 0715 0828 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 using 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. 

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. 

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). 

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 offset in time and in 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 x ls

(s) 

x 

(ns) 

y 

(ns/d) 

 T0

(MJD) 

Valid until 0000 on: 

(MJD) 

 Jun 06 -33 -293206.95 -38.8* 53887 53917 

 May 06 -33 -292004.15 -38.8 53856 53887* 

 Apr 06 -33 -291422.15 -38.8 53841 53856 

 Apr 06 -33 -290837.9 -38.95 53826 53841† 

 Mar 06 -33 -289630.45 -38.95 53795 53826 

 Feb 06 -33 -288539.85 -38.95 53767 53795 

 Jan 06 -33 -287838.75 -38.95 53749 53767 

 Jan 06 -33 -287330.45 -38.95 53736 53749 

 Dec 05 -32 -286118.35 -39.1 53705 53736 

 Nov 05 -32 -284937.85 -39.35 53675 53705 

 Oct 05 -32 -284308.25 -39.35 53659 53675 

 Oct 05 -32 -283721.75 -39.1 53644 53659† 

 Sep 05 -32 -283017.95 -39.1 53626 53644 

 Sep 05 -32 -282549.95 -39 53614 53626† 

 Aug 05 -32 -282081.95 -39 53602 53614 

 Aug 05 -32 -281350.45 -38.5 53583 53602† 

 Jul 05 -32 -280156.95 -38.5 53552 53583 

 Jun 05 -32 -279617.95 -38.5 53538 53552 

 Jun 05 -32 -278993.95 -39.0 53522 53538† 

 May 05 -32 -277784.95 -39.0 53491 53522 

 Apr 05 -32 -277160.95 -39.0 53475 53491 

 Apr 05 -32 -276613.55 -39.1 53461 53475† 

† Rate change in mid-month 

†† Rate change one day early 

*Provisional value