1

NIST TIME AND FREQUENCY BULLETIN 

NISTIR 6604-3

 NO. 520 MARCH 2001 

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

Email: bennett@boulder.nist.gov

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

with any correspondence regarding this bulletin. 

U.S. DEPARTMENT OF COMMERCE, Norman Y. Mineta, Secretary

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

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Karen H. Brown, Acting 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 all available common-view GPS satellites (see bibliography on page 5). UTC - UTC(NIST) data are on 

page 3.

 0000 HOURS COORDINATED UNIVERSAL TIME

FEB 2001 MJD UT1-UTC(NIST)

 (±5 ms)

UTC(USNO,MC) - UTC(NIST)

 (±20 ns)

1 51941 +77 ms 20 ns

8 51948 +76 ms 16 ns

15 51955 +69 ms 14 ns

22 51962 + 64 ms 8 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 rate of rotation of the Earth. 

NOTE: NO leap second will be inserted at the end of June 2001.

 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, and WWVB and are printed below. These corrections may be 

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

_______________________________________________________________________________________________________

+0.2 s beginning 0000 UTC 13 April 2000

DUT1 = UT1 - UTC = +0.1 s beginning 0000 UTC 19 October 2000

+0.0 s beginning 0000 UTC 01 March 2001
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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

Apr 5, 2000 51639 20

Apr 15, 2000 51649 20

Apr 25, 2000 51659 17

May 5, 2000 51669 17

May 15, 2000 51679 17

May 25, 2000 51689 18

June 4, 2000 51699 18

June 14, 2000 51709 20

June 24, 2000 51719 23

July 4, 2000 51729 24

July 14, 2000 51739 24

July 24, 2000 51749 24

Aug 3, 2000 51759 26

Aug 13, 2000 51769 25

Aug 23, 2000 51779 22

Sep 2, 2000 51789 12

Sep 12, 2000 51799 6

Sep 22, 2000 51809 0

Oct 2, 2000 51819 -8

Oct 12, 2000 51829 -13

Oct 22, 2000 51839 -19

Nov 1, 2000 51849 -25

Nov 11, 200- 51859 -22

Nov 21, 2000 51869 -21

Dec 1, 2000 51879 -16

Dec 11, 2000 51889 -9

Dec 21, 2000 51899 -5

Dec 31, 2000 51909 -3

Jan. 10, 2001 51919 2

Jan. 20, 2001 51929 7

Jan. 30, 2001 51939 11
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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 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)

02/01/01 51941 5.47 -237 +78

02/02/01 51942 5.49 +165 -220

02/03/01 51943 5.49 -102 -471

02/04/01 51944 5.49 +280 -192

02/05/01 51945 5.47 -110 +178

02/06/01 51946 5.49 -119 -253

02/07/01 51947 5.47 +287 +158

02/08/01 51948 5.47 +133 +330

02/09/01 51949 5.48 +56 -12

02/10/01 51950 5.48 +136 +326

02/11/01 51951 5.48 -458 -157

02/12/01 51952 5.48 +94 -45

02/13/01 51953 5.47 +27 +217

02/14/01 51954 5.47 -339 -266

02/15/01 51955 5.47 +171 -26

02/16/01 51956 5.50 -420 +224

02/17/01 51957 5.50 +219 +355

02/18/01 51958 5.50 -200 +40

02/19/01 51959 5.49 -353 -265

02/20/01 51960 5.48 -74 +119

02/21/01 51961 5.48 -291 +281

02/22/01 51962 5.49 +152 -240

02/23/01 51963 5.48 +433 +437

02/24/01 51964 5.49 -5 +16

02/25/01 51965 5.50 -383 -99

02/26/01 51966 5.50 +69 +8

02/27/01 51967 5.48 -11 -72

02/28/01 51968 5.49 -105 +15
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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 FEB

2001

 MJD Began 

UTC

Ended UTC Freq. FEB

2001

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 param e te rs th at are used to de fine UTC(NIST) w ith respe ct to our re al-tim e scale AT1. To find th e 

value of UTC(NIST)- AT1 at any tim e T (e xpressed as a M odifie d Julian D ay, including a fraction if ne e de d), th e 

appropriate eq uation to use is th e one for w h ich th e desire d T is gre ate r th an or e q ual to th e e ntry in th e T0

colum n and less th an th e e ntry in th e last colum n. Th e values of xls, x, and y for th at m onth are th e n use d in th e 

e q uation be low to find th e desire d value. Th e param e te rs x and y re prese nt th e offset in tim e and in fre q ue ncy, 

respe ctive ly, be tw e e n UTC(NIST) and AT1; th e param e te r xls is th e num be r of le ap seconds applie d to both 

UTC(NIST) and UTC as specifie d by th e IERS. Le ap seconds are not applie d to AT1.

Table 7.1

UTC(NIST)- AT1 = xls + x + y*(T - T0)

M onth xls

(s)

x

(ns)

y

(ns/d)

 T0

(M JD )

Valid until 0000 on:

(M JD )

Jul 9 9 -32 -19 2884.0 -41.0 51360 5139 1

Aug 9 9 -32 -19 4155.0 -41.0 5139 1 51422

Se p 9 9 -32 -19 5426.0 -40.5 51422 51452

O ct 9 9 -32 -19 6641.0 -40.5 51452 51483

Nov 9 9 -32 -19 789 6.5 -40.0 51483 51513

D e c 9 9 -32 -19 9 09 6.5 -40.0 51513† 51533

D e c 9 9 -32 -19 9 89 6.5 -41.0 51533 51544

Jan 00 -32 -200347.5 -40.5 51544 51575

Fe b 00 -32 -201603.0 -40.5 51575 51604

M ar 00 -32 -202777.5 -40.5 51604 51635

Apr 00 -32 -204033.0 -40.5 51635 51665

M ay 00 -32 -205248.0 -40.25 51665 5169 6

Jun 00 -32 -20649 5.75 -40.25 5169 6 51725††

Jul 00 -32 -207663.0 -40.0 51725†† 51757

Aug 00 -32 -2089 43.0 -39 .5 51757 51788

Se p 00 -32 -210167.5 -39 .0 51788 51818

O ct 00 -32 -211337.5 -39 .0 51818 51849

Nov 00 -32 -212546.5 -40.0 51849 51879

D e c 00 -32 -213746.5 -40.0 51879 519 10

Jan 01 -32 -2149 86.5 -40.0 519 10 519 41

Fe b 01 -32 -216226.5 -39 .0 519 41 519 69

M ar 01 -32 -217318.5 -39 .5 519 69 52000

Apr 01 -32 -218543.0 -39 .5* 52000 52030

†Rate ch ange in m id-m onth

††Rate ch ange one day e arly

*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.