NIST TIME AND FREQUENCY BULLETIN 

NIST IR 6653-05 

No. 605 May 2008

 

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

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, James M. Turner, Deputy Director 

 

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2 

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 2008 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

3 54559 -364 ms -13 ns 

10 54566 -373 ms -14 ns 

17 54573 -380 ms -15 ns 

24 54580 -388 ms -13 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. 

 NOTE: No leap second will be added at the end of June 2008. 

 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. 

 -0.4 s beginning 0000 UTC 13 March 2009 

 -0.3 s beginning 0000 UTC 29 November 2007 

DUT1 = UT1 - UTC = -0.2 s beginning 0000 UTC 14 June 2007 

 -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. 24, 2008 54549 -12.6 

Mar. 14, 2008 54539 -13.0 

Mar. 04, 2008 54529 -9.9 

Feb. 23, 2008 54519 -6.7 

Feb. 13, 2008 54509 -5.1 

Feb. 03, 2008 54499 -3.8 

Jan. 24, 2008 54489 -1.2 

Jan. 14, 2008 54479 -0.9 

Jan. 04, 2008 54469 1.3 

Dec. 25, 2007 54459 3.0 

Dec. 15, 2007 54449 5.2 

Dec. 05, 2007 54439 5.1 

Nov. 25, 2007 54429 7.1 

Nov. 15, 2007 54419 5.6 

Nov. 05, 2007 54409 5.8 

Oct. 26, 2007 54399 4.5 

Oct. 16, 2007 54389 2.3 

Oct. 06, 2007 54379 1.7 

Sep. 26, 2007 54369 1.2 

Sep. 16, 2007 54359 0.0 

Sep. 06, 2007 54349 -2.1 

Aug. 27, 2007 54339 -3.0 

Aug. 17, 2007 54329 -2.3 

Aug. 07, 2007 54319 -2.4 

Jul. 28, 2007 54309 -1.8 

Jul. 18, 2007 54299 -2.8 

Jul. 08, 2007 54289 -1.7 

 
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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) 

04/01/2008 54557 5. 65 +10 -1 

04/02/2008 54558 5. 65 -26 -33 

04/03/2008 54559 5. 65 -38 +19 

04/04/2008 54560 5. 65 -2 -5 

04/05/2008 54561 5. 65 -15 -7 

04/06/2008 54562 5. 65 +23 -9 

04/07/2008 54563 5. 65 +31 +27 

04/08/2008 54564 5. 65 -21 -18 

04/09/2008 54565 5. 65 -14 +17 

04/10/2008 54566 5. 65 +5 +9 

04/11/2008 54567 5. 65 +18 +3 

04/12/2008 54568 5. 65 -56 -7 

04/13/2008 54569 5. 65 +23 -3 

04/14/2008 54570 5. 65 +15 -15 

04/15/2008 54571 5. 65 +8 +16 

04/16/2008 54572 5. 65 -16 -16 

04/17/2008 54573 5. 65 +35 +30 

04/18/2008 54574 5. 65 +4 -13 

04/19/2008 54575 5. 65 +19 +12 

04/20/2008 54576 5. 65 +2 +3 

04/21/2008 54577 5. 65 -26 -9 

04/22/2008 54578 5. 65 -4 -14 

04/23/2008 54579 5. 65 +27 +24 

04/24/2008 54580 5. 65 -25 -21 

04/25/2008 54581 5. 65 -8 +2 

04/26/2008 54582 5. 65 -1 -3 

04/27/2008 54583 5. 65 +8 -1 

04/28/2008 54584 5. 65 +7 +4 

04/29/2008 54585 5. 65 +2 +15 

04/30/2008 54586 5. 65 +37 +8 
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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 

2008 

 MJD Began 

UTC 

Ended 

UTC 

Freq. Apr 

2008 

MJD Began 

 UTC 

End 

UTC 

WWVB 04-16-08 54572 0522 0618 60 kHz 

WWVB 04-09-08 54565 0710 0817 60 kHz 

WWVB 04-02-08 54558 1156 1236 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). 

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). 

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). 

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 x ls

(s) 

x 

(ns) 

y 

(ns/d) 

 T0

(MJD) 

Valid until 0000 on: 

(MJD) 

Jun 08 -33 -321208.7 -38.4* 54618 54648 

May 08 -33 -320018.3 -38.4 54587 54618* 

 Apr 08 -33 -319288.7 -38.4 54568 54587 

 Apr 08 -33 -318867.4 -38.3 54557 54568† 

 Mar 08 -33 -318178.0 -38.3 54539 54557 

 Mar 08 -33 -317684.0 -38.0 54526 54539† 

 Feb 08 -33 -316582.0 -38.0 54497 54526 

 Jan 08 -33 -315974.0 -38.0 54481 54497 

 Jan 08 -33 -315405.5 -37.9 54466 54481† 

 Dec 07 -33 -314230.6 -37.9 54424 54466 

 Nov 07 -33 -313813.7 -37.9 54435 54424 

 Nov 07 -33 -313091.7 -38.0 54405 54435† 

 Oct 07 -33 -312635.7 -38.0 54393 54405 

 Oct 07 -33 -311911.8 -38.1 54374 54393† 

 Sep 07 -33 -310768.8 -38.1 54344 54374 

 Aug 07 -33 -309587.7 -38.1 54313 54344 

 Jul 07 -33 -308940.0 -38.1 54296 54313 

 Jul 07 -33 -308408.0 -38.0 54282 54296† 

 Jun 07 -33 -307762.0 -38.0 54265 54282 

 Jun 07 -33 -30726.3 -37.9 54252 54265† 

 May 07 -33 -306738.7 -37.9 54238 54252 

 May 07 -33 -306091.0 -38.1 54221 54238† 

† Rate change in mid-month 

†† Rate change one day early 

*Provisional value