Clock differences at the Kunming and Urumqi stations in MJD57420. (a) Clock differences calculations based on GPS CV and VLBI respectively. (b) Clock difference series after removing the linear trend. (c) Clock difference series between the Kunming station clock and GPST across 20 days surrounding MJD57420. (d) Clock difference series between the Urumqi station clock and GPST across 20 days surrounding MJD57420.