1 

NIST TIME AND FREQUENCY BULLETIN 

 NISTIR 5082-5 

 NO. 498 MAY 1999 

 

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: 

 

Gwen E. Bennett, Editor 

Time and Frequency Division 

National Institute of Standards and Technology 

325 Broadway 

Boulder, CO 8O3O5-3328 

(3O3) 497-3295 

NOTE TO SUBSCRIBERS: Please include your address label (or a copy) 

with any correspondence regarding this bulletin. 

U.S. DEPARTMENT OF COMMERCE, William M. Daley, Secretary

TECHNOLOGY ADMINISTRATION, Gary R. Bachula, Acting Under Secretary of Commerce for Technology 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Karen Brown, Deputy Director 

 
2 

1. GENERAL BACKGROUND INFORMATION

_______________________________________________________________________________________________________ 

ACRONYMS AND ABBREVIATIONS USED IN THIS BULLETIN

BIPM - Bureau International des Poids et Mesures 

CCIR - International radio Consultative Committee 

Cs - Cesium standard 

GOES - Geostationary Operational Environmental Satellite 

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 1999 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

1 51269 +616 ms 4 ns 

8 51276 +607 ms -4 ns 

15 51283 +598 ms -9 ns 

22 51290 +588 ms -19 ns 

29 51297 +581 ms -27 ns 

 3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS 

 The master clock pulses used by the WWV, WWVH, WWVB and GOES 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 rate of 

rotation of the Earth. 

 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. There have been 22 leap seconds inserted in total. 

 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 GOES are printed below. These corrections 

may be added to received UTC time signals in order to obtain UT1. 

_______________________________________________________________________________________________________ 

 +0.7 s beginning 0000 UTC 01 January 1999 

DUT1 = UT1 - UTC = +0.6 s beginning 0000 UTC 04 March 1999 

 +0.5 s beginning 0000 UTC 27 May 1999 

 
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The deviation of 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 

May 6, 1998 50939 26 

May 16, 1998 50949 28 

May 26, 1998 50959 26 

June 5, 1998 50969 30 

June 15, 1998 50979 27 

June 25, 1998 50989 26 

July 5, 1998 50999 24 

July 15, 1998 51009 23 

July 25, 1998 51019 22 

Aug. 4, 1998 51029 15 

Aug. 14, 1998 51039 16 

Aug. 24, 1998 51049 11 

Sep. 3, 1998 51059 6 

Sep. 13, 1998 51069 1 

Sep. 23, 1998 51079 -4 

Oct. 3, 1998 51089 -7 

Oct. 13, 1998 51099 5 

Oct. 23, 1998 51109 -3 

Nov. 2, 1998 51119 -3 

Nov. 12, 1998 51129 -1 

Nov. 22, 1998 51139 0 

Dec. 2, 1998 51149 4 

Dec. 12, 1998 51159 3 

Dec. 22, 1998 51169 10 

Jan. 1, 1999 51179 10 

Jan. 11, 1999 51189 19 

Jan. 21, 1999 51199 22 

Jan. 31, 1999 51209 25 

Feb. 10, 1999 51219 25 

Feb. 20, 1999 51229 26 

Mar. 2, 1999 51239 24 

Mar. 12, 1999 51249 21 

Mar. 22, 1999 51259 15 
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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 (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 Dana, IN (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 (DANA) LORAN-C (FALLON) 

DATE MJD (μs) (8970) (9940) 

04/01/99 51269 5.74 -89 -186 

04/02/99 51270 5.75 +9 +64 

04/03/99 51271 5.76 -13 +217 

04/04/99 51272 5.77 +399 -29 

04/05/99 51273 5.79 +9 -475 

 

04/06/99 51274 5.64 -399 -244 

04/07/99 51275 5.64 +313 +469 

04/08/99 51276 5.62 -96 +235 

04/09/99 51277 5.59 -186 +323 

04/10/99 51278 5.58 (-) +560 

 

04/11/99 51279 5.56 +129 -351 

04/12/99 51280 5.56 +398 +573 

04/13/99 51281 5.74 +444 -301 

04/14/99 51282 5.77 -30 -235 

04/15/99 51283 5.76 -192 -69 

 

04/16/99 51284 5.76 +56 -192 

04/17/99 51285 5.75 +335 -160 

04/18/99 51286 5.75 -377 -333 

04/19/99 51287 5.75 +423 -112 

04/20/99 51288 5.73 +497 -38 

 

04/21/99 51289 5.78 -176 +0 

04/22/99 51290 5.75 +90 +40 

04/23/99 51291 5.73 -4 +138 

04/24/99 51292 5.73 +13 -221 

04/25/99 51293 5.73 -62 +120 

 

04/26/99 51294 5.75 -215 +109 

04/27/99 51295 5.75 +403 -275 

04/28/99 51296 5.75 +42 +109 

04/29/99 51297 5.76 +118 -300 

04/30/99 51298 5.73 -69 +310 

 
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4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES OF 5 MINUTES OR MORE 

 

PHASE PERTURBATIONS 

Station APR 

1999 

 MJD Began 

UTC 

Ended 

UTC 

Freq. APR 

1999 

MJD Began 

 UTC 

End 

UTC 

WWVB 04/23 51291 0640 0700 60 kHz 

WWVB 04/25 51293 1220 1300 60 kHz 

WWVB 04/26 51294 0530 0550 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-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 1 part in 1015. 

 The AT1 scale is run in real-time using 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 using 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 data available. 

 

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. and Weiss, M.A., "Accurate time and frequency transfer during common view of a GPS satellite," Proc. 34th 

 Annual Symposium on Frequency Control, p.334 (1980). 

Allan, D.W. and Barnes, J.A., "Optimal time and frequency using GPS signals," Proc. 36th Annual Symposium on 

 Frequency Control, p.378 (1982). 

Drullinger, R.E.; Glaze, D.J.; Lowe, J.P.; and Shirley, J.H., "The NIST optically pumped cesium frequency standard," 

 IEEE Trans. Instrum. Meas., IM-40, 162-164 (1991). 

Glaze, D.J.; Hellwig, H.; Allan, D.W.; and Jarvis, S., "NBS-4 and NBS-6: The NIST primary frequency standards," 

 Metrologia, Vol.13, pp.17-28 (1977). 

Wineland, D.J.; Allan, D.W.; Glaze, D.J.; Hellwig, H.; and Jarvis, S., "Results on limitations in primary cesium standard 

operation," IEEE Trans. Instrum. Meas., IM-25, pp.453-458 (1976).
 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) 

Jul 97 -31 -162435.0 -43.0 50630 50661 

Aug 97 -31 -163768.0 -43.0 50661 50692 

Sep 97 -31 -165101.0 -42.5 50692 50722 

Oct 97 -31 -166376.0 -42.0 50722 50753 

Nov 97 -31 -167678.0 -42.0 50753 50783 

Dec 97 -31 -168938.0 -42.5 50783 50814 

Jan 98 -31 -170255.0 -42.5 50814 50845 

Feb 98 -31 -171573.0 -42.5 50845 50873 

Mar 98 -31 -172763.0 -42.5 50873 50904 

Apr 98 -31 -174080.5 -42.0 50904 50934 

May 98 -31 -175340.5 -42.0 50934 50965 

Jun 98 -31 -176642.5 -41.5 50965 50995 

Jul 98 -31 -177887.5 -41.5 50995 51025 

Aug 98 -31 -179174.0 -41.0 51025 51057 

Sep 98 -31 -180445.0 -41.0 51057 51087 

Oct 98 -31 -181675.0 -41.5 51087 51118 

Nov 98 -31 -182961.5 -41.5 51118 51148 

Dec 98 -31 -184206.5 -41.5 51148 51179 

Jan 99 -32 -185493.0 -41.5 51179 51210 

Feb 99 -32 -186779.5 -41.5 51210 51238 

Mar 99 -32 -187927.5 -41.0 51238 51269 

Apr 99 -32 -189183.0 -40.5 51269 51299 

May 99 -32 -190383.0 -40.0 51299 51330 

Jun 99 -32 -191654.0 -41.0* 51330 51360 

*Provisional value 
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7. SPECIAL ANNOUNCEMENTS 

TRACEABLE FREQUENCY CALIBRATIONS 

(Now NVLAP Certified) 

 Anyone needing traceable frequency calibrations can get them by subscribing to the NIST Frequency 

Measurement and Analysis Service. This service is offered on a lease basis by NIST to provide an easy and inexpensive 

means to obtain traceability of a laboratory main oscillator and, in addition, to calibrate other devices in the lab. This 

service has been designed for ease of operation and as a practical lab calibration tool. 

 All the equipment and software needed are provided by NIST. Users must provide their own oscillator(s) and an 

ordinary telephone line so that NIST can access the system by modem. A total of four oscillators can be calibrated at the 

same time. Radio signals form either Loran-C or GPS satellite are used. Results for either are at about the same 

accuracy. 

 The calibration data are displayed in color and a graph is plotted daily for each oscillator connected. Data are 

also stored on disk. The user can call up any of the data and view them onscreen or in the form of plots. Many months of 

data can be plotted. 

 The system plots are easy to read and understand. The system manual is written for easy understanding and 

the NIST staff is available by telephone to assist. The modem connection allows NIST to access the data and to prepare 

a monthly traceability report which is mailed to the user. 

 Frequency sources of any accuracy can be calibrated. The FMAS is particularly useful at the highest levels of 

performance. This is because each user of the system contributes information and calibration data for the others. If an 

uncertainty arises, it is possible for NIST to call by modem to another user nearby. In this way problems in data 

interpretation can be resolved. 

 NVLAP certification requirements for frequency measurement are met by following the NIST-FMAS operating 

manual. This service does not eliminate the NVLAP audits but, when installed and operated per the NIST guidelines, 

audit requirements are easily met. 

 NIST retains title to the equipment and supplies any needed system spares. Equipment that fails is replaced by 

overnight shipment. Training for use of the system is available if requested by the user. 

 The NIST Frequency Measurement and Analysis Service provides a complete solution to nearly all frequency 

measurement and calibration problems. For a free information package, please contact Michael Lombardi at (30) 497-

3212, email at lombardi@boulder.nist.gov, or write to: Michael Lombardi, NIST, Division 847, 325 Broadway, Boulder, CO 

 80303. 

________________________________________________________________________________________________