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U.S. NAVAL OBSERVATORY
WASHINGTON, D.C. 20392-5420 

							July 23, 1998
							No. 64
TIME SERVICE ANNOUNCEMENT SERIES 14

UTC TIME STEP

1. The International Earth Rotation Service (IERS) has announced the introduction of a time step to occur at the end of December, 1998.

2. Coordinated Universal Time (UTC) will be retarded by 1.0s so that the sequence of dates of the UTC markers will be: 

1998 December 31   23h   59m   59s
1998 December 31   23h   59m   60s
1999 January  01    0h    0m    0s
3. The difference between UTC and International Atomic Time (TAI) is: 
from 1997   01 Jul, UTC to 1999 01 January, UTC:	TAI-UTC= +31s
from 1999   01 Jan, UTC until further notice:		TAI-UTC= +32s
4. The insertion of one leap second will be evident by the change of sign of the DUT1 correction which will become positive. Extrapolated values of DUT1 are distributed weekly in the IERS Bulletin A.

5. All coordinated time scales will be affected by this adjustment. However, Loran-C and GPS will not be adjusted physically. Times of Coincidence for LORAN-C are available on the Time Service Web Page (http://tycho.usno.navy.mil/loran.html). For GPS, the leap second correction contained within the UTC data of subframe 4, page 18 of the navigation message transmitted by satellites will change. 
	Before the leap second
	GPS-UTC = +12 (i.e., GPS is ahead of UTC by twelve seconds)

	After the leap second
	GPS-UTC = +13s (i.e., GPS will be ahead by thirteen seconds)



						DENNIS D. McCARTHY
						Director
						Directorate of Time

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