1

NIST TIME AND FREQUENCY BULLETIN 

NISTIR 5091-5

 NO. 510 MAY 2000 

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, Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Raymond G. Kammer, Director
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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 up to 10 GPS satellites (see bibliography on page 5). UTC - UTC(NIST) data are on page 3.

 0000 HOURS COORDINATED UNIVERSAL TIME

APR 2000 MJD UT1-UTC(NIST)

 (±5 ms)

UTC(USNO,MC) - UTC(NIST)

 (±20 ns)

6 51640 +271 ms 14 ns

13 51647 +264 ms 12 ns

20 51654 +255 ms 12 ns

27 51661 +249 ms 11 ns

NOTE: It has been announced that there will be no leap second introduced at the end of June 2000. 

 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 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. 

_______________________________________________________________________________________________________

+0.4 s beginning 0000 UTC 14 October 1999

DUT1 = UT1 - UTC = +0.3 s beginning 0000 UTC 06 January 2000

+0.2 s beginning 0000 UTC 13 April 2000
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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 31, 1999 51329 -16

Jun 10, 1999 51339 -16

Jun 20, 1999 51349 -14

Jun 30, 1999 51359 -12

Jul 10, 1999 51369 -6

Jul 20, 1999 51379 -3

Jul 30, 1999 51389 -1

Aug 9, 1999 51399 -2

Aug 19, 1999 51409 4

Aug 29, 1999 51419 12

Sep 8, 1999 51429 15

Sep 18, 1999 51439 13

Sep 28, 1999 51449 15

Oct 8, 1999 51459 9

Oct 18, 1999 51469 9

Oct 29, 1999 51479 10

Nov 7, 1999 51489 7

Nov 17, 1999 51499 6

Nov 27, 1999 51509 -1

Dec 7, 1999 51519 -1

Dec 17, 1999 51529 -5

Dec 27, 1999 51539 -3

Jan 6, 2000 51549 0

Jan 16, 2000 51559 2

Jan 26, 2000 51569 0

Feb 5, 2000 51579 6

Feb 15, 2000 51589 5

Feb 25, 2000 51599 7

Mar 6, 2000 51609 8

Mar 16, 2000 51619 15

Mar 26, 2000 51629 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 unce rtainty 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 master stations monitored are Dana, IN (8970) 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)

04/01/00 51635 5.73 -287 -328

04/02/00 51636 5.71 +485 -30

04/03/00 51637 5.71 -332 -34

04/04/00 51638 5.73 -324 -488

04/05/00 51639 5.74 -175 +255

04/06/00 51640 5.73 +205 +322

04/07/00 51641 5.72 +229 +36

04/08/00 51642 5.72 +413 -293

04/09/00 51643 5.71 +103 -364

04/10/00 51644 5.72 -305 -384

04/11/00 51645 5.72 +428 -156

04/12/00 51646 5.74 -365 +103

04/13/00 51647 5.74 -223 -499

04/14/00 51648 5.75 -35 +117

04/15/00 51649 5.74 -406 +409

04/16/00 51650 5.73 -147 +226

04/17/00 51651 5.73 +469 -191

04/18/00 51652 5.74 +208 -229

04/19/00 51653 5.68 -57 +119

04/20/00 51654 5.66 -468 -439

04/21/00 51655 5.68 +304 +415

04/22/00 51656 5.68 +197 -300

04/23/00 51657 5.68 (-) +233

04/24/00 51658 5.67 +214 -60

04/25/00 51659 5.66 +218 -10

04/26/00 51660 5.66 +52 -89

04/27/00 51661 5.65 +140 +45

04/28/00 51662 5.66 +100 -261

04/29/00 51663 5.66 -148 -151

04/30/00 51664 5.67 -277 +197
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4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES OF 5 MINUTES OR MORE

WWVB 60 kHz

PHASE PERTURBATIONS

Station APR

2000

 MJD Began 

UTC

Ended UTC Freq. APR

2000

MJD Began

 UTC

End

UTC

WWVB

WWV

WWVH

5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS

Primary frequency standards developed and maintained by NIST are used to provide accuracy (rate) input to the BIPM. NIST-7, which 

had served as the U.S. primary standard since 1994, has been replaced by NIST-F1, a cesium fountain frequency standard. The 

uncertainty of the new standard is currently 1.7 parts 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 

very 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 (September 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 (December 1976). 
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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 98 -32 -177887.5 -41.5 50995 51025

Aug 98 -32 -179174.0 -41.0 51025 51057

Sep 98 -32 -180445.0 -41.0 51057 51087

Oct 98 -32 -181675.0 -41.5 51087 51118

Nov 98 -32 -182961.5 -41.5 51118 51148

Dec 98 -32 -184206.5 -41.5 51148 51179

Jan 99 -32 -185493.0 -41.5 51179 51210

Feb 99 -32 -186779.5 -41.0 51210 51238

Mar 99 -32 -187927.5 -40.5 51238 51269

Apr 99 -32 -189183.0 -40.0 51269 51299

May 99 -32 -190383.0 -41.0 51299 51330

Jun 99 -32 -191654.0 -41.0 51330 51360

Jul 99 -32 -192884.0 -41.0 51360 51391

Aug 99 -32 -194155.0 -41.0 51391 51422

Sep 99 -32 -195426.0 -40.5 51422 51452

Oct 99 -32 -196641.0 -40.5 51452 51483

Nov 99 -32 -197896.5 -40.0 51853 51513

Dec 99 -32 -199096.5 -40.0 51513 51533†

Dec 99 -32 -199896.5 -41.0 51533 51544

Jan 00 -32 -200347.5 -40.5 51544 51575

Feb 00 -32 -201603.0 -40.5 51575 51604

Mar 00 -32 -202777.5 -40.5 51604 51635

Apr 00 -32 -204033.0 -40.5 51635 51665

May 00 -32 -205248.0 -40.5 51665 51696

Jun 00 -32 -206495.75 -40.25* 51696 51726*

† Rate change in mid-month

†† Rate change one day early

*Provisional value
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IMPORTANT NOTICE!

The Time and Frequency Bulletin data are now online at

http://tf.nist.gov

7. SPECIAL ANNOUNCEMENTS 

TRACEABLE FREQUENCY CALIBRATIONS

(Now NVLAP Certified)

Laboratories can get any needed traceable frequency calibrations 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 frequency standard and, in addition, to calibrate other devices in the lab. This 

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

All necessary hardware and software is 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 maximum total of five oscillators can be calibrated 

at the same time. Radio signals from GPS satellites are used and the measurement uncertainty is 

±2 x 10-13 per day. Any frequency from 1 Hz to 120 MHz (in 1 Hz increments) can be measured.

The calibration data are displayed in color, and a graph is plotted daily for each oscillator. 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. Up to 5 months of data can be 

plotted on one graph.

The system plots are easy to read and understand. The system manual is written clearly and the NIST staff are

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. All necessary replacement parts are 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 phone Michael Lombardi at (303) 497-3212,

or E-mail him at lombardi@boulder.nist.gov, or write to Michael Lombardi, NIST, Division 847, 325 Broadway, Boulder, CO 

80305.