No: 2023-10 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] 60188 2023-09-01 +7 +114 60189 2023-09-02 +8 +119 60190 2023-09-03 +8 +122 60191 2023-09-04 +8 +117 60192 2023-09-05 +9 +115 60193 2023-09-06 +9 +122 60194 2023-09-07 +10 +124 60195 2023-09-08 +10 +124 60196 2023-09-09 +9 +130 60197 2023-09-10 +9 +131 60198 2023-09-11 +7 +130 60199 2023-09-12 +5 +128 60200 2023-09-13 +5 +134 60201 2023-09-14 +3 +131 60202 2023-09-15 +4 +130 60203 2023-09-16 +5 +129 60204 2023-09-17 +6 +134 60205 2023-09-18 +8 +138 60206 2023-09-19 +9 +134 60207 2023-09-20 +10 +129 60208 2023-09-21 +9 +132 60209 2023-09-22 +8 +131 60210 2023-09-23 +8 +134 60211 2023-09-24 +9 +136 60212 2023-09-25 +8 +137 60213 2023-09-26 +5 +142 60214 2023-09-27 +5 +138 60215 2023-09-28 +7 +131 60216 2023-09-29 +9 +138 60217 2023-09-30 +11 +136 Statistical precision of the GPS data : +/- 2 ns (reported at 1 sigma). Statistical precision of the GLONASS data : +/- 20 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 September 2023 is (1 + 0,2 E-14) +/- 3,5 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