[TAI - GPS time] and [UTC - 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 2002 MJD C0/ns s/ns [s/sqrt(N)]/ns 0h UTC _________________________________________________________ Jan 1 52275 -8 - - Jan 2 52276 -9 - - Jan 3 52277 -2 5 1 Jan 4 52278 3 6 1 Jan 5 52279 6 - - Jan 6 52280 8 5 1 Jan 7 52281 11 4 1 Jan 8 52282 14 5 1 Jan 9 52283 9 4 1 Jan 10 52284 8 4 1 Jan 11 52285 4 5 1 Jan 12 52286 7 6 1 Jan 13 52287 4 4 1 Jan 14 52288 1 5 1 Jan 15 52289 -2 7 1 Jan 16 52290 -4 5 1 Jan 17 52291 -7 4 1 Jan 18 52292 -7 6 1 Jan 19 52293 -6 5 1 Jan 20 52294 -5 5 1 Jan 21 52295 -7 5 1 Jan 22 52296 -9 6 1 Jan 23 52297 -10 6 1 Jan 24 52298 -8 7 1 Jan 25 52299 -6 4 1 Jan 26 52300 0 5 1 Jan 27 52301 0 7 1 Jan 28 52302 0 4 1 Jan 29 52303 1 6 1 Jan 30 52304 -5 5 1 Jan 31 52305 -6 5 1 Feb 1 52306 -5 5 1 Feb 2 52307 -1 7 1 Feb 3 52308 -1 6 1 Feb 4 52309 -2 5 1 Feb 5 52310 0 6 1 Feb 6 52311 4 6 1 Feb 7 52312 7 5 1 Feb 8 52313 3 6 1 Feb 9 52314 0 5 1 Feb 10 52315 1 5 1 Feb 11 52316 3 4 1 Feb 12 52317 3 5 1 Feb 13 52318 3 5 1 Feb 14 52319 -2 5 1 Feb 15 52320 -4 6 1 Feb 16 52321 -5 6 1 Feb 17 52322 -1 6 1 Feb 18 52323 -1 6 1 Feb 19 52324 -3 6 1 Feb 20 52325 -3 5 1 Feb 21 52326 -3 6 1 Feb 22 52327 -1 6 1 Feb 23 52328 2 5 1 Feb 24 52329 4 5 1 Feb 25 52330 7 4 1 Feb 26 52331 9 6 1 Feb 27 52332 13 5 1 Feb 28 52333 12 6 1 Mar 1 52334 7 5 1 Mar 2 52335 0 6 1 Mar 3 52336 0 6 1 Mar 4 52337 -4 - - Mar 5 52338 -3 5 1 Mar 6 52339 -3 5 1 Mar 7 52340 -7 5 1 Mar 8 52341 -7 4 1 Mar 9 52342 -7 5 1 Mar 10 52343 -5 6 1 Mar 11 52344 -2 6 1 Mar 12 52345 -4 6 1 Mar 13 52346 0 5 1 Mar 14 52347 5 4 1 Mar 15 52348 4 5 1 Mar 16 52349 4 7 1 Mar 17 52350 6 5 1 Mar 18 52351 5 4 1 Mar 19 52352 1 6 1 Mar 20 52353 -1 7 1 Mar 21 52354 0 5 1 Mar 22 52355 4 5 1 Mar 23 52356 3 6 1 Mar 24 52357 6 7 1 Mar 25 52358 11 5 1 Mar 26 52359 8 5 1 Mar 27 52360 7 6 1 Mar 28 52361 4 6 1 Mar 29 52362 5 5 1 Mar 30 52363 3 6 1 Mar 31 52364 2 7 1 Apr 1 52365 0 5 1 Apr 2 52366 -1 5 1 Apr 3 52367 -1 6 1 Apr 4 52368 4 6 1 Apr 5 52369 5 6 1 Apr 6 52370 5 4 1 Apr 7 52371 6 5 1 Apr 8 52372 0 5 1 Apr 9 52373 -4 5 1 Apr 10 52374 -4 8 1 Apr 11 52375 -3 4 1 Apr 12 52376 -3 5 1 Apr 13 52377 -5 4 1 Apr 14 52378 -3 6 1 Apr 15 52379 -1 6 1 Apr 16 52380 0 6 1 Apr 17 52381 3 4 1 Apr 18 52382 -1 4 1 Apr 19 52383 0 6 1 Apr 20 52384 1 6 1 Apr 21 52385 3 6 1 Apr 22 52386 0 4 1 Apr 23 52387 1 5 1 Apr 24 52388 -1 5 1 Apr 25 52389 -3 7 1 Apr 26 52390 -5 6 1 Apr 27 52391 -4 7 1 Apr 28 52392 -4 7 1 Apr 29 52393 -5 6 1 Apr 30 52394 -2 5 1 May 1 52395 -3 4 1 May 2 52396 -3 5 1 May 3 52397 -5 4 1 May 4 52398 -6 4 1 May 5 52399 -5 4 1 May 6 52400 -4 5 1 May 7 52401 -1 5 1 May 8 52402 4 6 1 May 9 52403 2 5 1 May 10 52404 4 6 1 May 11 52405 1 8 1 May 12 52406 1 5 1 May 13 52407 -4 6 1 May 14 52408 -6 6 1 May 15 52409 -6 4 1 May 16 52410 -4 5 1 May 17 52411 -6 4 1 May 18 52412 -1 4 1 May 19 52413 1 4 1 May 20 52414 2 6 1 May 21 52415 2 5 1 May 22 52416 3 6 1 May 23 52417 1 6 1 May 24 52418 1 5 1 May 25 52419 -4 5 1 May 26 52420 -3 4 1 May 27 52421 -5 5 1 May 28 52422 -3 6 1 May 29 52423 -6 5 1 May 30 52424 -7 5 1 May 31 52425 -2 4 1 Jun 1 52426 -3 - - Jun 2 52427 -3 4 1 Jun 3 52428 -3 5 1 Jun 4 52429 -1 5 1 Jun 5 52430 -1 4 1 Jun 6 52431 1 7 1 Jun 7 52432 4 5 1 Jun 8 52433 -2 5 1 Jun 9 52434 -1 4 1 Jun 10 52435 -3 3 1 Jun 11 52436 -3 4 1 Jun 12 52437 -3 4 1 Jun 13 52438 -1 6 1 Jun 14 52439 -1 5 1 Jun 15 52440 -2 4 1 Jun 16 52441 -2 5 1 Jun 17 52442 -6 5 1 Jun 18 52443 -9 6 1 Jun 19 52444 -4 - - Jun 20 52445 2 4 1 Jun 21 52446 -4 5 1 Jun 22 52447 -2 4 1 Jun 23 52448 1 4 1 Jun 24 52449 -1 5 1 Jun 25 52450 -7 5 1 Jun 26 52451 -10 5 1 Jun 27 52452 -12 7 1 Jun 28 52453 -11 5 1 Jun 29 52454 -14 5 1 Jun 30 52455 -12 2 1 Jul 1 52456 -16 3 1 Jul 2 52457 -17 2 1 Jul 3 52458 -14 2 1 Jul 4 52459 -12 2 1 Jul 5 52460 -11 3 1 Jul 6 52461 -11 3 1 Jul 7 52462 -14 3 1 Jul 8 52463 -8 9 2 Jul 9 52464 -6 3 1 Jul 10 52465 -6 3 1 Jul 11 52466 -5 3 1 Jul 12 52467 -3 3 1 Jul 13 52468 -5 3 1 Jul 14 52469 -6 3 1 Jul 15 52470 -8 3 1 Jul 16 52471 -11 3 1 Jul 17 52472 -13 4 1 Jul 18 52473 -14 4 1 Jul 19 52474 -14 4 1 Jul 20 52475 -19 3 1 Jul 21 52476 -18 4 1 Jul 22 52477 -15 3 1 Jul 23 52478 -13 3 1 Jul 24 52479 -13 3 1 Jul 25 52480 -12 3 1 Jul 26 52481 -12 3 1 Jul 27 52482 -14 11 2 Jul 28 52483 -13 3 1 Jul 29 52484 -9 3 1 Jul 30 52485 -10 3 1 Jul 31 52486 -10 3 1 Aug 1 52487 -7 3 1 Aug 2 52488 -9 3 1 Aug 3 52489 -12 3 1 Aug 4 52490 -13 3 1 Aug 5 52491 -12 3 1 Aug 6 52492 -14 3 1 Aug 7 52493 -16 3 1 Aug 8 52494 -17 3 1 Aug 9 52495 -14 3 1 Aug 10 52496 -12 3 1 Aug 11 52497 -12 3 1 Aug 12 52498 -9 3 1 Aug 13 52499 -7 3 1 Aug 14 52500 -7 3 1 Aug 15 52501 -4 3 1 Aug 16 52502 -3 3 1 Aug 17 52503 -3 3 1 Aug 18 52504 -6 3 1 Aug 19 52505 -10 4 3 Aug 20 52506 -12 4 1 Aug 21 52507 -11 4 1 Aug 22 52508 -12 4 1 Aug 23 52509 -9 4 1 Aug 24 52510 -7 3 1 Aug 25 52511 -5 3 1 Aug 26 52512 -2 4 1 Aug 27 52513 -5 3 1 Aug 28 52514 -8 3 1 Aug 29 52515 -6 3 1 Aug 30 52516 -11 2 1 Aug 31 52517 -11 3 1 Sep 1 52518 -11 3 1 Sep 2 52519 -15 3 1 Sep 3 52520 -14 4 1 Sep 4 52521 -16 3 1 Sep 5 52522 -15 3 1 Sep 6 52523 -14 4 1 Sep 7 52524 -14 3 1 Sep 8 52525 -11 2 1 Sep 9 52526 -12 3 1 Sep 10 52527 -11 3 1 Sep 11 52528 -8 4 1 Sep 12 52529 -6 3 1 Sep 13 52530 -5 2 1 Sep 14 52531 -3 5 1 Sep 15 52532 -1 6 1 Sep 16 52533 2 3 1 Sep 17 52534 1 4 1 Sep 18 52535 -1 3 1 Sep 19 52536 0 4 1 Sep 20 52537 -3 4 1 Sep 21 52538 -4 3 1 Sep 22 52539 -10 3 1 Sep 23 52540 -12 4 1 Sep 24 52541 -16 3 1 Sep 25 52542 -15 3 1 Sep 26 52543 -15 3 1 Sep 27 52544 -14 3 1 Sep 28 52545 -11 3 1 Sep 29 52546 -9 3 1 Sep 30 52547 -7 4 1 Oct 1 52548 -7 3 1 Oct 2 52549 -4 3 1 Oct 3 52550 -3 3 1 Oct 4 52551 -5 4 1 Oct 5 52552 -3 3 1 Oct 6 52553 -6 3 1 Oct 7 52554 -10 3 1 Oct 8 52555 -10 3 1 Oct 9 52556 -6 3 1 Oct 10 52557 -6 3 1 Oct 11 52558 -6 4 1 Oct 12 52559 -10 3 1 Oct 13 52560 -11 3 1 Oct 14 52561 -14 4 1 Oct 15 52562 -17 4 1 Oct 16 52563 -16 4 1 Oct 17 52564 -13 4 1 Oct 18 52565 -14 4 1 Oct 19 52566 -12 4 1 Oct 20 52567 -10 3 1 Oct 21 52568 -8 4 1 Oct 22 52569 -11 3 1 Oct 23 52570 -13 4 1 Oct 24 52571 -11 4 1 Oct 25 52572 -6 4 1 Oct 26 52573 -2 - - Oct 27 52574 -5 3 1 Oct 28 52575 -9 3 1 Oct 29 52576 -11 3 1 Oct 30 52577 -13 3 1 Oct 31 52578 -14 3 1 Nov 1 52579 -15 3 1 Nov 2 52580 -12 3 1 Nov 3 52581 -16 4 1 Nov 4 52582 -16 4 1 Nov 5 52583 -14 4 1 Nov 6 52584 -9 3 1 Nov 7 52585 -5 3 1 Nov 8 52586 -6 - - Nov 9 52587 -5 3 1 Nov 10 52588 -4 5 1 Nov 11 52589 -5 4 1 Nov 12 52590 -7 4 1 Nov 13 52591 -5 3 1 Nov 14 52592 -6 3 1 Nov 15 52593 -11 3 1 Nov 16 52594 -13 3 1 Nov 17 52595 -13 3 1 Nov 18 52596 -17 3 1 Nov 19 52597 -19 3 1 Nov 20 52598 -17 3 1 Nov 21 52599 -16 4 1 Nov 22 52600 -12 3 1 Nov 23 52601 -7 3 1 Nov 24 52602 -8 3 1 Nov 25 52603 -6 3 1 Nov 26 52604 -8 3 1 Nov 27 52605 -11 3 1 Nov 28 52606 -6 3 1 Nov 29 52607 -7 3 1 Nov 30 52608 -7 3 1 Dec 1 52609 -3 3 1 Dec 2 52610 -5 3 1 Dec 3 52611 -5 3 1 Dec 4 52612 -6 3 1 Dec 5 52613 -8 3 1 Dec 6 52614 -1 2 1 Dec 7 52615 2 3 1 Dec 8 52616 4 3 1 Dec 9 52617 11 3 1 Dec 10 52618 13 3 1 Dec 11 52619 15 3 1 Dec 12 52620 16 3 1 Dec 13 52621 13 3 1 Dec 14 52622 11 3 1 Dec 15 52623 11 3 1 Dec 16 52624 8 2 1 Dec 17 52625 5 3 1 Dec 18 52626 7 3 1 Dec 19 52627 5 4 1 Dec 20 52628 2 3 1 Dec 21 52629 -8 3 1 Dec 22 52630 -7 3 1 Dec 23 52631 -5 3 1 Dec 24 52632 -4 3 1 Dec 25 52633 -2 3 1 Dec 26 52634 -1 2 1 Dec 27 52635 -3 3 1 Dec 28 52636 -3 3 1 Dec 29 52637 -4 2 1 Dec 30 52638 -11 3 1 Dec 31 52639 -11 2 1 _________________________________________________________