NIST TIME AND FREQUENCY BULLETIN 

NIST IR 6646-05 

NO. 593 MAY 2007

 

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 M. GUTIERREZ, Secretary

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

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, William Jeffrey, 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 

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 2007 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

 5 54195 -071 ms 16 ns 

 12 54202 -079 ms 15 ns 

19 54209 -094 ms 16 ns 

26 54216 -102 ms 15 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. 

 -0.6 s beginning 0000 UTC 17 March 2005 

DUT1 = UT1 - UTC = +0.3 s beginning 0000 UTC 01 January 2006 

+0.2 s beginning 0000 UTC 27 April 2006 

+0.1 s beginning 0000 UTC 28 September 2006 

+0.0 s beginning 0000 UTC 22 December 2006 

 -0.1 s beginning 0000 UTC 15 March 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. 30, 2007 54189 12.5 

Mar. 20, 2007 54179 13.6 

Mar. 10, 2007 54169 15.2 

Feb. 28, 2007 54159 15.2 

Feb. 18, 2007 54149 15.3 

Feb. 08, 2007 54139 14.0 

Jan. 29, 2007 54129 13.3 

Jan. 19, 2007 54119 15.5 

Jan. 09, 2007 54109 16.1 

Dec. 30, 2006 54099 15.9 

Dec. 20, 2006 54089 15.5 

Dec. 10, 2006 54079 14.5 

Nov. 30, 2006 54069 11.6 

Nov. 20, 2006 54059 9.8 

Nov. 10, 2006 54049 2.7 

Oct. 31, 2006 54039 -4.9 

Oct. 21, 2006 54029 -11.8 

Oct. 11, 2006 54019 -14.3 

Oct. 01, 2006 54009 -14.4 

Sep. 21, 2006 53999 -13.0 

Sep. 11, 2006 53989 -8.8 

Sep. 01, 2006 53979 -5.4 

Aug. 22, 2006 53969 -0.2 

Aug. 12, 2006 53959 2.3 

Aug. 02, 2006 53949 4.2 

Jul. 23, 2006 53939 6.7 

Jul. 13, 2006 53929 8.6 

Jul. 03, 2006 53919 8.3 

 
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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) 

04/01/2007 54191 5. 65 +31 +20

04/02/2007 54192 5. 65 +78 -13

04/03/2007 54193 5. 65 +7 +17

04/04/2007 54194 5. 65 -87 -1

04/05/2007 54195 5. 65 +84 +7

04/06/2007 54196 5. 65 -29 +17

04/07/2007 54197 5. 65 -63 +35

04/08/2007 54198 5. 65 -1 -10

04/09/2007 54199 5. 65 +100 -40

04/10/2007 54200 5. 65 -103 +35

04/11/2007 54201 5. 65 +20 +9 

04/12/2007 54202 5. 65 +44 -20 

04/13/2007 54203 5. 65 -42 +25 

04/14/2007 54204 5. 65 +68 -22 

04/15/2007 54205 5. 65 +24 +14 

04/16/2007 54206 5. 65 -33 -44 

04/17/2007 54207 5. 65 -8 -29 

04/18/2007 54208 5. 65 +31 +29 

04/19/2007 54209 5. 65 +62 -30 

04/20/2007 54210 5. 65 +9 +22 

04/21/2007 54211 5. 65 -12 -22 

04/22/2007 54212 5. 65 -31 -5 

04/23/2007 54213 5. 65 -2 -80 

04/24/2007 54214 5. 65 -15 +50 

04/25/2007 54215 5. 65 +0 +8 

04/26/2007 54216 5. 65 +9 +2 

04/27/2007 54217 5. 65 +2 -18 

04/28/2007 54218 5. 65 +33 +13 

04/29/2007 54219 5. 65 +8 +3 

04/30/2007 54220 5. 65 -42 +1 
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4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS 

OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS 

2 ms 

Station APR 

2007 

 MJD Began 

UTC 

Ended 

UTC 

Freq. APR 

2007 

MJD Began 

 UTC 

End 

UTC 

WWVB 4-26-07 54216 2237 2258 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 xls

(s) 

x 

(ns) 

y 

(ns/d) 

 T0

(MJD) 

Valid until 0000 on: 

(MJD) 

 Jun 07 -33 -307272.1 -38.1* 54252 54282 

 May 07 -33 -306091.0 -38.1 54221 54252* 

 Apr 07 -33 -304951.6 -38.3 54191 54221 

 Mar 07 -33 -304262.2 -38.1 54173 54191 

 Mar 07 -33 -303764.3 -38.3 54160 54173† 

 Feb 07 -33 -302691.9 -38.3 54132 54160 

 Jan 07 -33 -302079.1 -38.3 54116 54132 

 Jan 07 -33 -301501.6 -38.5 54101 54116† 

 Dec 06 -33 -300847.1 -38.5 54084 54101 

 Dec 06 -33 -300303.9 -38.8 54070 54084† 

 Nov 06 -33 -299799.5 -38.8 54057 54070 

 Nov 06 -33 -299129.7 -39.4 54040 54057† 

 Oct 06 -33 -298459.9 -39.4 54023 54040 

 Oct 06 -33 -297916.7 -38.8 54009 54023† 

 Sep 06 -33 -297606.3 -38.8 54001 54009 

 Sep 06 -33 -296759.3 -38.5 53979 54001† 

 Aug 06 -33 -295565.8 -38.5 53948 53979 

 Jul 06 -33 -294911.3 -38.5 53931 53948 

 Jul 06 -33 -294368.80 -38.75 53917 53931† 

 Jun 06 -33 -293206.30 -38.75 53887 53917 

 May 06 -33 -292702.55 -38.75 53874 53887 

 May 06 -33 -292004.15 -38.8 53856 53874† 

† Rate change in mid-month 

†† Rate change one day early 

*Provisional value