NIST TIME AND FREQUENCY BULLETIN 

 NISTIR 6630-05 

 NO. 557 MAY 2004 

 

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 

 

7. SPECIAL ANNOUNCEMENTS............................................................................................................... 7 

 

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, DONALD L. EVANS, Secretary

TECHNOLOGY ADMINISTRATION, Phillip J. Bond, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Arden L. Bement, Jr., 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 

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 2004 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

1 53068 -434 ms 4 ns 

8 53075 -443 ms 10 ns 

15 53082 -447 ms 14 ns 

22 53089 -453 ms 17 ns 

29 53124 -452 ms 18 ns 

CORRECTION: The data for UTC(USNO,MC) was incorrectly reported as negative in the bulletin posted 5/3/04. 

 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. 

NOTE: No leap second will be added at the end of June 2004.

 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, and 1998. 

 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. 

_______________________________________________________________________________________________________ 

+0.0 s beginning 0000 UTC 01 March 2001 

 -0.1 s beginning 0000 UTC 04 October 2001 

DUT1 = UT1 - UTC = -0.2 s beginning 0000 UTC 14 February 2002 

 -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 

 
3 

 

The difference between UTC(NIST) from 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 in Circular T. 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(NIST) ns 

Mar. 25, 2004 53089 6.3 

Mar. 15, 2004 53079 4.1 

Mar. 05, 2004 53069 3.2 

Feb. 24, 2004 53059 1.2 

Feb. 14, 2004 53049 -2.0 

Feb. 4, 2004 53039 -4.5 

Jan. 25, 2004 53029 -4.6 

Jan. 15, 2004 53019 -4.2 

Jan. 5, 2004 53009 -3.1 

Dec. 26, 2003 52999 -4.0 

Dec. 16, 2003 52989 -2.8 

Dec. 6, 2003 52979 -0.2 

Nov. 26, 2003 52969 -1.1 

Nov. 16, 2003 52959 2.0 

Nov. 6, 2003 52949 2.1 

Oct. 27, 2003 52939 1.8 

Oct. 17, 2003 52929 1.2 

Oct. 7, 2003 52919 3.9 

Sep. 27, 2003 52909 7.9 

Sep. 17, 2003 52899 7.5 

Sep. 7, 2003 52889 7.6 

Aug. 28, 2003 52879 7.7 

Aug. 18, 2003 52869 8.0 

Aug. 8, 2003 52859 10.2 

Jul. 29, 2003 52849 10.7 

Jul. 19, 2003 52839 12.7 

Jul. 9, 2003 52829 12.6 

Jun. 29, 2003 52819 9.2 

Jun. 19, 2003 52809 7.5 

Jun. 9, 2003 52799 3.8 

 
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 (in ns). 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, ND 

(8970-Y) and Fallon, NV (9940). 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 (FALLON) 

DATE MJD (μs) (8970) (9940) 

04/01/04 53096 5.67 -37 -160 

04/02/04 53097 5.69 -9 +228 

04/03/04 53098 5.70 +161 +437 

04/04/04 53099 5.70 -41 +161 

04/05/04 53100 5.70 -55 +366 

04/06/04 53101 5.71 +2 -295 

04/07/04 53102 5.71 -66 +406 

04/08/04 53103 5.69 +54 -135 

04/09/04 53104 5.70 +111 -256 

04/10/04 53105 5.70 +26 -403 

04/11/04 53106 5.69 +5 +393 

04/04/04 53107 5.69 -71 +219 

04/13/04 53108 5.70 -26 +83 

04/14/04 53109 5.71 -55 +104 

04/15/04 53110 5.71 -0 +110 

04/16/04 53111 5.71 -32 +16 

04/17/04 53112 5.71 +10 +150 

04/18/04 53113 5.71 -18 +12 

04/19/04 53114 5.71 +52 +274 

04/20/04 53115 5.72 +17 +119 

04/21/04 53116 5.71 +42 +18 

04/22/04 53117 5.71 -78 +46 

04/23/04 53118 5.71 +52 -55 

04/24/04 53119 5.71 -33 -497 

04/25/04 53120 5.72 +27 -235 

04/26/04 53121 5.71 +16 -37 

04/27/04 53122 5.71 +36 -161 

04/28/04 53123 5.71 -10 +399 

04/29/04 53124 5.72 -3 -458 

04/30/04 53125 5.73 +4 -206 
5 

 

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS 

2 ms 

Station APR 

2004 

 MJD Began 

UTC 

Ended 

UTC 

Freq. APR 

2004 

MJD Began 

 UTC 

End 

UTC 

WWVB 60 kHz 

WWVB 

WWV 

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-7 was 

the U.S. primary standard from 1994 to 1999, when it was replaced by NIST-F1, a cold-atom cesium fountain frequency standard. 

The uncertainty of NIST-F1 is currently about 1 part in 1015. 

 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. 

Shirley, J.H.; Lee, W.D.; Drullinger, R.E.; “Accuracy evaluation of the primary frequency standard NIST-7,” Metrologia, Vol. 38, pp. 

427-458, (2001). 

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) 

 May 04 -32 -264731.4 -39.25* 53157* 53187 

 May 04 -32 -263514.65 -39.25 53126 53157* 

 Apr 04 -32 -263004.4 -39.25 53113 53126 

 Apr 04 -32 -262334.6 -39.4 53096 53113† 

 Mar 04 -32 -261783.0 -39.4 53082 53096 

 Mar 04 -32 -261110.65 -39.55 53065 53082† 

 Feb 04 -32 -259963.7 -39.55 53036 53065 

 Jan 04 -32 -259410.0 -39.55 53022 53036 

 Jan 04 -32 -258738.5 -39.5 53005 53022† 

 Dec 03 -32 -258343.5 -39.5 52995 53005 

 Dec 03 -32 -257516.1 -39.4 52974 52995† 

 Nov 03 -32 -256925.1 -39.4 52959 52974 

 Nov 03 -32 -256334.85 -39.35 52944 52959† 

 Oct 03 -32 -255783.95 -39.35 52930 52944 

 Oct 03 -32 -255112.45 -39.5 52913 52930† 

 

 Sep 03 -32 -253927.745 -39.5 52883 52913 

 Aug 03 -32 -252702.95 -39.5 52852 52883 

 Jul 03 -32 -252228.95 -39.5 52840 52852 

 Jul 03 -32 -251473.7 -39.75 52821 52840† 

 Jun 03 -32 -251076.2 -39.75 52811 52821 

 Jun 03 -32 -250276.2 -40.0 52791 52811† 

 May 03 -32 -249652.2 -39.0 52775 52791 

 May 03 -32 -249052.2 -40.0 52760 52775† 

 Apr 03 -32 -248495.7 -39.75 52746 52760 

 Apr 03 -32 -247855.7 -40.0 52730 52746† 

† Rate change in mid-month 

†† Rate change one day early 

*Provisional value 
7

 

7. SPECIAL ANNOUNCEMENTS 

NOTICE TO DISCONTINUE INVOLVEMENT WITH GOES TIME CODE SERVICE 

NIST has announced that it will discontinue its involvement with the time code broadcast from the GOES 

WEST and GOES EAST satellites operated by the National Oceanic and Atmosphere Administration 

(NOAA) on January 1, 2005. This decision has been jointly made by NIST and NOAA in response to the 

fact that nearly all users requiring time more accurate than 1 ms now use the Global Positioning System 

(GPS), and as a result, commercial sources for GOES timing receivers no longer exist. 

NOAA is expected to continue to provide a GOES time code indefinitely after January 1, 2005, and existing 

receivers should be able to continue to receive and decode the time signal. However, the time code will no 

longer be controlled and checked by NIST, and the received time is expected to be less accurate when NIST 

discontinues its involvement. The GOES satellites currently broadcast continuously updated position 

information in addition to the time, so that GOES receivers can automatically correct for path delay changes 

caused by satellite motion. This allows the current system to have a time uncertainty of less than 100 ms. 

NOAA is expected to continuously broadcast a fixed position from the satellites, which could increase the 

time uncertainty to 1 ms or more. 

The GOES time broadcasts began in 1974 and have served many applications and thousands of users. 

NIST will continue to control and monitor the time code through January 1, 2005 to allow users who require 

a high accuracy signal sufficient time to replace their existing receivers. If you have additional questions, 

please contact Michael Lombardi, 303-497-3212, or email lombardi@boulder.nist.gov.