NISTIR 8104-05

NIST Time and Frequency Bulletin

Karen Hansen Lichtfuss, Editor

http://dx.doi.org/10.6028/NIST.IR.8104-05
NISTIR 8104-05

NIST Time and Frequency Bulletin

Karen Hansen Lichtfuss, Editor 

Time and Frequency Division 

Physical Measurement Laboratory 

http://dx.doi.org/10.6028/NIST.IR.8104-05

May 2016 

U.S. Department of Commerce 

Penny Pritzker, Secretary

National Institute of Standards and Technology 

Willie E. May, Under Secretary of Commerce for Standards and Technology and Director 
1 

NIST TIME AND FREQUENCY BULLETIN 

NIST IR 8104-05

No. 702 May 2016

1. GENERAL BACKGROUND INFORMATION........................................................................................... 2 

2. TIME SCALE INFORMATION ............................................................................................................... 2 

3. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB

 PHASE PERTURBATIONS..................................................................................................................... 4 

4. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS........................................................... 4 

5. UTC (NIST) – AT1 PARAMETERS .......................................................................................................... 5 

This bulletin is published monthly. Address correspondence to: 

Karen Hansen Lichtfuss, Editor 

Time and Frequency Division 

National Institute of Standards and Technology

325 Broadway 

Boulder, CO 8O3O5-3328 

(3O3) 497-3295

Email: karen.hansenlichtfuss@nist.gov

U.S. DEPARTMENT OF COMMERCE, Penny Pritzker, Secretary

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Willie E. May, Under Secretary of Commerce for 

Standards and Technology and Director
2 

1. GENERAL BACKGROUND INFORMATION _______________________________________________________________________________________________________________________________

ACRONYMS AND ABBREVIATIONS USED IN THIS BULLETIN 

ACTS - Automated Computer Time Service

BIPM - Bureau International des Poids et Mesures

GPS - Global Positioning System

IERS - International Earth Rotation Service

MC - Master Clock

MJD - Modified Julian Date

NIST - National Institute of Standards and Technology 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

UT1 - Universal Time (Astronomical) 

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 

April 2016 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

7 57485

14

21 57499

28 57506

 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 period of rotation. 

NOTE: No leap second will be added at the end of June 2016. 

 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 time 

scale on 30 June 1972, 1981-1983, 1985, 1992-1994, 1997, 2012, 2015 and on 31 December 1972-1979, 1987, 1989, 

1990,1995, 1998, 2005, 2008. 

 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 the received UTC time signals in order to obtain UT1.

DUT1 = UT1 - UTC = 

-0.1 s beginning 0000 UTC 24 March 2016

+0.0 s beginning 0000 UTC 31 January 2016

+0.1 s beginning 0000 UTC 26 November 2015

+0.2 s beginning 0000 UTC 11 September 2015

+0.3 s beginning 0000 UTC 01 July 2015

-0.7 s beginning 0000 UTC 28 May 2015

-0.6 s beginning 0000 UTC 19 March 2015

-0.5 s beginning 0000 UTC 25 December 2014

-0.4 s beginning 0000 UTC 25 September 2014

-0.3 s beginning 0000 UTC 08 May 2014

- 0.2 s beginning 0000 UTC 20 February 2014

- 0.1 s beginning 0000 UTC 21 November 2013

+0.0 s beginning 0000 UTC 22 August 2013

+0.1 s beginning 0000 UTC 11 April 2013

+0.2 s beginning 0000 UTC 31 January 2013

+0.3 s beginning 0000 UTC 25 October 2012

+0.4 s beginning 0000 UTC 01 July 2012

57492

- 4 ns

- 4 ns

- 2 ns

- 1 ns

- 94 ms

- 108 ms

- 120 ms

- 130 ms
DATE MJD UTC-UTC(NIST), ns

Mar. 22, 2016 57469 2.8

Mar. 12, 2016 57459 0.9

Mar. 2, 2016 57449 -0.4

Feb. 11, 2016 57439 -4.9

Feb. 11, 2016 57429 -7.6

Feb. 01, 2016 57419 -8.6

Jan. 22, 2016 57409 -7.4

Jan. 12, 2016 57399 -3.0

Jan. 02, 2016 57389 1.7

Dec. 23, 2015 57379 3.5

Dec. 13, 2015 57369 4.3

Dec. 03, 2015 57359 6.4

Nov. 23, 2015 57349 5.8

Nov. 13, 2015 57339 4.8

Nov. 3, 2015 57329 5.3

Oct. 24, 2015 57319 9.6

Oct. 14, 2015 57309 13.9

Oct. 4, 2015 57299 16.1

Sep. 24, 2015 57289 15.8

Sep. 14, 2015 57279 14.3

Set. 4, 2015 57269 13.6

Aug. 25, 2015 57259 13.5

Aug. 15, 2105 57249 13.0

Aug. 5, 2015 57239 11.2

Jul. 26, 2015 57229 9.4

Jul. 16, 2015 57219 8.8

Jul. 6, 2015 57209 7.7

Jun. 26, 2015 57199 6.6

Jun. 16, 2015 57189 6.3

Jun. 6, 2015 57179 5.8

0000 Hours Coordinated Universal Time

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 ten-day intervals. Five-day interval data are available in Circular T . 

 3
4

3. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS

2 ms

Station Apr.

2016

 MJD Began 

UTC

Ended 

UTC

Freq. Apr.

2016 MJD Began

UTC

End

UTC

WWVB 04/06/16

04/05/16

04/03/16

57484

57483

57481

2352

2156

0034

2245

60kHz

60kHz

60kHz

None

WWV None

None

WWVH None

None

4. 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 and to 

provide the best possible realization of the SI second. NIST-F1 and NIST F-2, cold-atom cesium fountain frequency standards, have

served as the U.S. primary standards of time and frequency since 1999. The uncertainty of NIST-F2 is currently about 1 part 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 by use of 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. 

References:

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).
Month xls

(s)

x

(ns)

y

(ns/d)

 T0

(MJD)

Valid until 0000 on:

(MJD)

Jun 16 -36 -431923.7 -37.1* 57540 57570

May 16 -36 -431476.7 -37.25† 57528 57540*

May 16 -36 -430771.8 -37.1 57509 57528

Apr 16 -36 -430697.6 -37.1† 57507 57509

Apr 16 -36 -429931.05 -36.5† 57486 57507

Apr 16 -36 -429672.75 -36.9 57479 57486

Mar 16 -36 -428636.75 -37.0† 57451 57479

Mar 16 -36 -428521.05 -37.3 57448 57451

Feb 16 -36 -427816.15 -37.3† 57429 57448

Feb 16 -36 -427556.45 -37.1† 57422 57429

Feb 16 -36 -427446.05 -36.8 57419 57422

Jan 16 -36 -427014.25 -36.8† 57408 57419

Jan 16 -36 -426313.25 -36.4 57388 57408

† Rate change in mid-month

*Provisional value

The table below 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 Date, 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 offsets in time and 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.

5. UTC(NIST) – AT1 PARAMETERS

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

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