[UTC - GPS time] and [TAI - GPS time] The GPS satellites disseminate a common time scale designated 'GPS time'. The relation between GPS time and TAI is [TAI - GPS time] = 19 s + C0, where the time difference of 19 seconds is kept constant and C0 is a quantity of the order of tens of nanoseconds, varying with time. The relation between GPS time and UTC involves a variable number of seconds as a consequence of the leap seconds of the UTC system and is as follows: from 1999 January 1, 0h UTC until further notice: [UTC - GPS time] = -13 s + C0. Here C0 is given at 0h UTC every day. C0 is computed as follows. The GPS data recorded at the Paris Observatory for highest-elevation satellites are first corrected for precise satellite ephemerides and for ionospheric delays derived from IGS maps, and then smoothed to obtain daily values of [UTC(OP) - GPS time] at 0h UTC. Daily values of C0 are then derived by linear interpolation of [UTC - UTC(OP)]. The combined standard uncertainty of the daily C0 values is of the order of 10 ns. TABLE: Calculated values of C0. s: standard deviation characterizing the dispersion of individual measurements; N: the number of measurements. _________________________________________________________ Date 2001 MJD C0/ns s/ns [s/sqrt(N)]/ns 0h UTC _________________________________________________________ Jan 1 51910 -12 5 1 Jan 2 51911 -13 4 1 Jan 3 51912 -11 5 1 Jan 4 51913 -9 5 1 Jan 5 51914 -8 5 1 Jan 6 51915 -6 6 1 Jan 7 51916 -6 6 1 Jan 8 51917 -8 5 1 Jan 9 51918 -9 5 1 Jan 10 51919 -11 6 1 Jan 11 51920 -12 4 1 Jan 12 51921 -11 5 1 Jan 13 51922 -10 6 1 Jan 14 51923 -8 7 1 Jan 15 51924 -6 5 1 Jan 16 51925 -4 4 1 Jan 17 51926 -3 5 1 Jan 18 51927 -1 4 1 Jan 19 51928 -1 6 1 Jan 20 51929 -1 5 1 Jan 21 51930 -3 5 1 Jan 22 51931 -6 6 1 Jan 23 51932 -11 6 1 Jan 24 51933 -13 5 1 Jan 25 51934 -13 6 1 Jan 26 51935 -11 4 1 Jan 27 51936 -10 5 1 Jan 28 51937 -9 5 1 Jan 29 51938 -10 4 1 Jan 30 51939 -11 6 1 Jan 31 51940 -12 6 1 Feb 1 51941 -12 4 1 Feb 2 51942 -7 6 1 Feb 3 51943 -8 5 1 Feb 4 51944 -10 5 1 Feb 5 51945 -5 6 1 Feb 6 51946 -5 5 1 Feb 7 51947 -2 6 1 Feb 8 51948 -3 5 1 Feb 9 51949 -5 7 1 Feb 10 51950 -7 5 1 Feb 11 51951 -7 4 1 Feb 12 51952 -10 6 1 Feb 13 51953 -12 13 2 Feb 14 51954 -12 6 1 Feb 15 51955 -11 6 1 Feb 16 51956 -10 4 1 Feb 17 51957 -8 5 1 Feb 18 51958 -8 6 1 Feb 19 51959 -6 6 1 Feb 20 51960 -7 7 1 Feb 21 51961 -11 7 1 Feb 22 51962 -10 4 1 Feb 23 51963 -11 5 1 Feb 24 51964 -13 5 1 Feb 25 51965 -15 4 1 Feb 26 51966 -16 6 1 Feb 27 51967 -16 7 1 Feb 28 51968 -15 5 1 Mar 1 51969 -14 5 1 Mar 2 51970 -11 7 1 Mar 3 51971 -10 4 1 Mar 4 51972 -10 7 1 Mar 5 51973 -10 5 1 Mar 6 51974 -10 8 2 Mar 7 51975 -10 7 1 Mar 8 51976 -11 5 1 Mar 9 51977 -12 6 1 Mar 10 51978 -13 5 1 Mar 11 51979 -13 5 1 Mar 12 51980 -13 4 1 Mar 13 51981 -15 6 1 Mar 14 51982 -15 8 1 Mar 15 51983 -17 6 1 Mar 16 51984 -16 6 1 Mar 17 51985 -15 6 1 Mar 18 51986 -14 6 1 Mar 19 51987 -12 4 1 Mar 20 51988 -11 5 1 Mar 21 51989 -10 6 1 Mar 22 51990 -8 4 1 Mar 23 51991 -7 6 1 Mar 24 51992 -7 5 1 Mar 25 51993 -8 5 1 Mar 26 51994 -8 7 1 Mar 27 51995 -7 4 1 Mar 28 51996 -5 5 1 Mar 29 51997 -2 5 1 Mar 30 51998 -1 6 1 Mar 31 51999 0 9 2 Apr 1 52000 -2 7 3 Apr 2 52001 2 9 3 Apr 3 52002 0 5 1 Apr 4 52003 -1 6 1 Apr 5 52004 -3 8 1 Apr 6 52005 -9 5 1 Apr 7 52006 -13 5 1 Apr 8 52007 -12 7 1 Apr 9 52008 -10 5 1 Apr 10 52009 -16 6 1 Apr 11 52010 -17 7 1 Apr 12 52011 -18 7 1 Apr 13 52012 -14 7 1 Apr 14 52013 -11 7 1 Apr 15 52014 -15 7 1 Apr 16 52015 -16 10 1 Apr 17 52016 -17 5 1 Apr 18 52017 -14 6 1 Apr 19 52018 -16 5 1 Apr 20 52019 -10 6 1 Apr 21 52020 -6 8 1 Apr 22 52021 5 5 1 Apr 23 52022 8 6 1 Apr 24 52023 9 7 1 Apr 25 52024 13 5 1 Apr 26 52025 12 5 1 Apr 27 52026 12 6 1 Apr 28 52027 17 6 1 Apr 29 52028 17 4 1 Apr 30 52029 15 7 1 May 1 52030 11 6 1 May 2 52031 6 7 1 May 3 52032 0 6 1 May 4 52033 0 5 1 May 5 52034 -8 6 1 May 6 52035 -11 5 1 May 7 52036 -10 5 1 May 8 52037 -12 7 1 May 9 52038 -13 7 1 May 10 52039 -15 6 1 May 11 52040 -17 6 1 May 12 52041 -12 11 2 May 13 52042 -7 7 1 May 14 52043 -11 6 1 May 15 52044 -6 8 1 May 16 52045 2 7 1 May 17 52046 0 7 1 May 18 52047 1 4 1 May 19 52048 2 5 1 May 20 52049 0 7 1 May 21 52050 -3 6 1 May 22 52051 -2 5 1 May 23 52052 1 5 1 May 24 52053 -1 5 1 May 25 52054 2 6 1 May 26 52055 8 7 1 May 27 52056 8 5 1 May 28 52057 11 6 1 May 29 52058 13 8 2 May 30 52059 7 5 1 May 31 52060 5 5 1 Jun 1 52061 8 5 1 Jun 2 52062 9 5 1 Jun 3 52063 4 6 1 Jun 4 52064 0 5 1 Jun 5 52065 -4 5 1 Jun 6 52066 -3 6 1 Jun 7 52067 -1 6 1 Jun 8 52068 4 5 1 Jun 9 52069 6 8 1 Jun 10 52070 7 6 1 Jun 11 52071 9 6 1 Jun 12 52072 12 7 1 Jun 13 52073 13 6 1 Jun 14 52074 14 7 1 Jun 15 52075 10 5 1 Jun 16 52076 9 6 1 Jun 17 52077 3 7 1 Jun 18 52078 0 5 1 Jun 19 52079 1 7 1 Jun 20 52080 -2 6 1 Jun 21 52081 -6 4 1 Jun 22 52082 -7 5 1 Jun 23 52083 -2 6 1 Jun 24 52084 -1 10 1 Jun 25 52085 4 6 1 Jun 26 52086 4 5 1 Jun 27 52087 7 7 1 Jun 28 52088 8 5 1 Jun 29 52089 11 8 1 Jun 30 52090 14 5 1 Jul 1 52091 18 6 1 Jul 2 52092 20 5 1 Jul 3 52093 21 5 1 Jul 4 52094 21 5 1 Jul 5 52095 20 5 1 Jul 6 52096 20 5 1 Jul 7 52097 16 5 1 Jul 8 52098 17 4 1 Jul 9 52099 15 6 1 Jul 10 52100 17 5 1 Jul 11 52101 21 6 1 Jul 12 52102 21 6 1 Jul 13 52103 23 7 1 Jul 14 52104 25 4 1 Jul 15 52105 23 5 1 Jul 16 52106 21 5 1 Jul 17 52107 16 6 1 Jul 18 52108 15 4 1 Jul 19 52109 12 7 1 Jul 20 52110 12 6 1 Jul 21 52111 14 5 1 Jul 22 52112 13 6 1 Jul 23 52113 15 7 1 Jul 24 52114 14 5 1 Jul 25 52115 13 6 1 Jul 26 52116 11 6 1 Jul 27 52117 9 6 1 Jul 28 52118 8 4 1 Jul 29 52119 9 7 1 Jul 30 52120 2 6 1 Jul 31 52121 2 6 1 Aug 1 52122 2 9 1 Aug 2 52123 6 11 2 Aug 3 52124 10 8 1 Aug 4 52125 10 8 1 Aug 5 52126 14 6 1 Aug 6 52127 18 12 2 Aug 7 52128 20 8 1 Aug 8 52129 17 5 1 Aug 9 52130 16 6 1 Aug 10 52131 17 5 1 Aug 11 52132 13 5 1 Aug 12 52133 9 7 1 Aug 13 52134 5 8 1 Aug 14 52135 2 6 1 Aug 15 52136 0 7 1 Aug 16 52137 -3 8 1 Aug 17 52138 -2 7 1 Aug 18 52139 0 9 1 Aug 19 52140 0 7 1 Aug 20 52141 1 7 1 Aug 21 52142 3 5 1 Aug 22 52143 9 5 1 Aug 23 52144 14 6 1 Aug 24 52145 14 6 1 Aug 25 52146 15 6 1 Aug 26 52147 20 8 1 Aug 27 52148 25 5 1 Aug 28 52149 22 4 1 Aug 29 52150 24 4 1 Aug 30 52151 22 28 4 Aug 31 52152 19 17 3 Sep 1 52153 14 9 1 Sep 2 52154 12 6 1 Sep 3 52155 14 6 1 Sep 4 52156 13 5 1 Sep 5 52157 8 7 1 Sep 6 52158 6 5 1 Sep 7 52159 6 4 1 Sep 8 52160 6 5 1 Sep 9 52161 6 6 1 Sep 10 52162 7 7 1 Sep 11 52163 11 7 1 Sep 12 52164 11 6 1 Sep 13 52165 11 6 1 Sep 14 52166 10 5 1 Sep 15 52167 13 5 1 Sep 16 52168 14 6 1 Sep 17 52169 16 7 1 Sep 18 52170 17 5 1 Sep 19 52171 13 4 1 Sep 20 52172 9 5 1 Sep 21 52173 10 6 1 Sep 22 52174 8 6 1 Sep 23 52175 7 7 1 Sep 24 52176 8 7 1 Sep 25 52177 2 6 1 Sep 26 52178 4 5 1 Sep 27 52179 3 5 1 Sep 28 52180 3 6 1 Sep 29 52181 1 7 1 Sep 30 52182 5 6 1 Oct 1 52183 4 6 1 Oct 2 52184 4 6 1 Oct 3 52185 8 7 1 Oct 4 52186 10 5 1 Oct 5 52187 16 5 1 Oct 6 52188 18 6 1 Oct 7 52189 16 5 1 Oct 8 52190 15 6 1 Oct 9 52191 12 6 1 Oct 10 52192 7 5 1 Oct 11 52193 6 5 1 Oct 12 52194 9 5 1 Oct 13 52195 7 5 1 Oct 14 52196 8 7 1 Oct 15 52197 12 6 1 Oct 16 52198 10 5 1 Oct 17 52199 9 5 1 Oct 18 52200 12 4 1 Oct 19 52201 8 4 1 Oct 20 52202 7 6 1 Oct 21 52203 9 7 1 Oct 22 52204 10 8 1 Oct 23 52205 9 6 1 Oct 24 52206 7 5 1 Oct 25 52207 9 5 1 Oct 26 52208 9 7 1 Oct 27 52209 11 6 1 Oct 28 52210 12 7 3 Oct 29 52211 9 6 3 Oct 30 52212 3 4 1 Oct 31 52213 -2 5 1 Nov 1 52214 -2 5 1 Nov 2 52215 -3 4 1 Nov 3 52216 -2 5 1 Nov 4 52217 1 4 1 Nov 5 52218 0 6 1 Nov 6 52219 2 5 1 Nov 7 52220 3 5 1 Nov 8 52221 3 6 1 Nov 9 52222 9 5 1 Nov 10 52223 11 7 1 Nov 11 52224 13 5 1 Nov 12 52225 14 4 1 Nov 13 52226 17 5 1 Nov 14 52227 16 5 1 Nov 15 52228 19 5 1 Nov 16 52229 18 4 1 Nov 17 52230 16 4 1 Nov 18 52231 11 5 1 Nov 19 52232 8 5 1 Nov 20 52233 6 5 1 Nov 21 52234 2 6 1 Nov 22 52235 2 5 1 Nov 23 52236 0 6 1 Nov 24 52237 0 6 1 Nov 25 52238 0 5 1 Nov 26 52239 -1 6 1 Nov 27 52240 0 4 1 Nov 28 52241 2 5 1 Nov 29 52242 2 4 1 Nov 30 52243 2 4 1 Dec 1 52244 0 5 1 Dec 2 52245 -3 5 1 Dec 3 52246 1 5 1 Dec 4 52247 5 7 1 Dec 5 52248 6 4 1 Dec 6 52249 3 5 1 Dec 7 52250 6 6 1 Dec 8 52251 6 4 1 Dec 9 52252 10 6 1 Dec 10 52253 12 4 1 Dec 11 52254 9 5 1 Dec 12 52255 3 5 1 Dec 13 52256 5 5 1 Dec 14 52257 1 3 0 Dec 15 52258 -2 4 1 Dec 16 52259 0 5 1 Dec 17 52260 3 6 1 Dec 18 52261 3 5 1 Dec 19 52262 1 5 1 Dec 20 52263 0 6 1 Dec 21 52264 2 5 1 Dec 22 52265 -1 5 1 Dec 23 52266 0 5 1 Dec 24 52267 -1 5 1 Dec 25 52268 0 5 1 Dec 26 52269 -2 4 1 Dec 27 52270 -4 4 1 Dec 28 52271 -3 5 1 Dec 29 52272 0 5 1 Dec 30 52273 -1 5 1 Dec 31 52274 -2 6 1 _________________________________________________________