No: 202505 STANDARD TIME & FREQUENCY SERVICE BULLETIN NATIONAL METROLOGY INSTITUTE OF SOUTH AFRICA CONTENTS 1. Measured values of NMISA - GNSS system time 2. Normalised mean frequency of UTC(ZA) 3. Other time distribution services 4. Leap second adjustments 5. Relation between time scales _________________________________________________________________________________________ 1. Measured values of NMISA - GNSS system time. The following measurements are the time differences between NMISA's prediction of UTC and the prediction of UTC disseminated by Global Navigation Satellite System (GNSS). The results are the linear fit to data points gathered using the All-in-View methodology based on a tracking schedule referenced to MJD 50722 (1 October 1997). The differences are reported for 00:00 UTC. MJD DATE ZA-GPS ZA-GLONASS [ns] [ns] 60766 2025-04-01 -4 +67 60767 2025-04-02 -9 +68 60768 2025-04-03 -4 +74 60769 2025-04-04 -8 +66 60770 2025-04-05 -11 +68 60771 2025-04-06 -10 +68 60772 2025-04-07 -9 +70 60773 2025-04-08 -9 +66 60774 2025-04-09 -11 +68 60775 2025-04-10 -11 +70 60776 2025-04-11 -11 +69 60777 2025-04-12 -8 +71 60778 2025-04-13 -7 +73 60779 2025-04-14 -3 +69 60780 2025-04-15 -1 +74 60781 2025-04-16 +4 +74 60782 2025-04-17 +4 +77 60783 2025-04-18 +9 +78 60784 2025-04-19 +10 +82 60785 2025-04-20 +8 +88 60786 2025-04-21 +10 +92 60787 2025-04-22 +10 +94 60788 2025-04-23 +13 +90 60789 2025-04-24 +11 +93 60790 2025-04-25 +11 +98 60791 2025-04-26 +10 +100 60792 2025-04-27 +12 +93 60793 2025-04-28 +14 +96 60794 2025-04-29 +16 +93 60795 2025-04-30 +19 +97 Statistical precision of the GPS data : +/- 2 ns (reported at 1 sigma). Statistical precision of the GLONASS data : +/- 10 ns (reported at 1 sigma). Current master clock: T4Science iMaser 3000 (serial number 112) hydrogen maser _________________________________________________________________________________________ 2. Normalised mean frequency of UTC(ZA). The predicted normalised mean frequency of UTC(ZA) for April 2025 is (1 + 1,0 E-14) +/- 5,5 E-14 (for a level of confidence of 95,45%) _________________________________________________________________________________________ 3. Other time distribution services. NMISA operates a NTP server that is available for use by other NTP servers. (Please do not use this server to synchronise individual computers.) The address is time.nmisa.org. The accuracy of this server is typically within +/- 0,5 ms at the source, but the received user accuracy will depend on factors like network delay, network symmetry, as well as the computer hardware and software. _________________________________________________________________________________________ 4. Leap second adjustments. From time to time, for the purpose of keeping the UTC time scale within +/- 0,9 s of the UT1 astronomical time scale, a leap second is introduced. Positive leap seconds beginning at 23:59:60 UTC and ending 00:00:00 UTC, were inserted in the UTC time scale on the following Dates: 30 June 1972 31 December 1972 31 December 1973 31 December 1974 31 December 1975 31 December 1976 31 December 1977 31 December 1978 31 December 1979 30 June 1981 30 June 1982 30 June 1983 30 June 1985 31 December 1987 31 December 1989 31 December 1990 30 June 1992 30 June 1993 30 June 1994 31 December 1995 30 June 1997 31 December 1998 31 December 2005 31 December 2008 30 June 2012 30 June 2015 31 December 2016 _________________________________________________________________________________________ 5. Relation between time scales. The relation between time scales (as from 1 January 2017, 0h UTC till further notice): TAI - UTC = 37 s UTC - GPS = -18 s with TAI : International Atomic Time, UTC : Coordinated Universal Time and GPS : Global Positioning System. _________________________________________________________________________________________ NB: For specific applications or more detail on the presented data or analysis of the data, please contact the Time and Frequency project at the address shown below. National Metrology Institute of South Africa Time and Frequency Metrology Private Bag X34 Lynnwood Ridge 0040 South Africa Telephone: (012) 947 2800 Telephone (International) +27 12 947 2800 Web page: http://time.nmisa.org