## 3 Assessment of Precise MGEX Orbit and Clock Products
### Clock Comparisons  
Satellite clocks were compared at 5-min intervals. The comparison results were aligned with a reference satellite by satellite differencing to remove systematic biases. The STD values of the aligned comparison results were used as indicators of clock quality. Differences that were three times larger than the medians of the series were regarded as outliers and excluded from the comparison results. Figure 6 shows the clock consistency of Galileo and QZSS with respect to ESM. The mean STD of clock differences is given in Tables 6 and 7. The points on the horizontal axes in Figure 6 represent outliers that were excluded from the statistics. For the Galileo satellites, the mean STD values of clock differences were around 0.1 ns among COD, ESM, GRG and WUM. However, SHA showed the largest mean STD value of clock differences, which was at the 0.5 ns level. Further, it is interesting to notice that the number of outliers of GFZ was obviously larger than those of other products during the periods of March and April, which may indicate that GFZ changed strategies when estimating Galileo clocks during the periods. As for J01, the clock differences were mostly at the 0.2- to 0.3-ns level, while GFZ showed large differences of about 1 ns when compared with other products. Again, the clock differences increased dramatically during and after switching the attitude mode to ON. As a result, clock differences during the ON period were excluded when calculating the statistics shown in Table 7. For J02 and J03, COD showed the best agreement with ESM at the 0.3-ns level. For J07, the STD value of clock differences between WUM and GFZ was 0.40 ns. Likewise, the quality of BDS-2 and BDS-3 clock products was assessed using individual satellites rather than averaging all of them. Figure 7 shows the satellite-specific clock differences with respect to WUM, and the mean STD values are given in Table 8 according to different orbit types. For BDS-2 GEOs, the STD values of clock differences reached up to 1.06 ns for GFZ and 1.26 ns for SHA with respect to WUM. Obviously, smaller STD values between 0.2 and 0.5 ns could be observed among COD, ESM, GFZ and WUM for BDS-2 IGSO/MEO clocks. SHA showed the largest STDs of BDS-2 IGSO/MEO clocks at the 1.1-ns level. For BDS-3 MEO clocks, the STD values of clock differences between ESM and WUM were mostly at the 0.2- to 0.3-ns level. One may notice that the clock differences for C35, \begin{table}
\begin{tabular}{c|c c c c c c} \hline \hline  & **COD** & **ESM** & **GFZ** & **JAX** & **TUM** & **WUM** \\ \hline \multirow{3}{*}{COD} & J01 & - & 14.4 & 75.6 & 14.7 & 36.9 & 23.3 \\  & J02 & - & 15.2 & 39.3 & - & 44.5 & 36.0 \\  & J03 & - & 10.8 & 32.6 & - & 24.6 & 34.2 \\ \hline \multirow{3}{*}{ESM} & J01 & & - & 78.6 & 15.6 & 31.4 & 19.2 \\  & J02 & & - & 41.0 & - & 41.3 & 31.6 \\  & J03 & & - & 38.3 & - & 29.8 & 36.1 \\ \hline \multirow{3}{*}{GFZ} & J01 & & - & 78.0 & 88.4 & 81.2 \\  & J02 & & - & - & 51.4 & 28.6 \\  & J03 & & - & - & 55.3 & 29.9 \\ \hline JAX & J01 & & & - & 39.0 & 18.1 \\ \hline \multirow{3}{*}{TUM} & J01 & & & & - & 33.9 \\  & J02 & & & & - & 40.4 \\ \cline{1-1}  & J03 & & & & - & 43.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: 3D RMS of QZSS IGSO orbit comparisons (units: cm). C36 and C37 were comparatively larger than for other BDS-3 satellites. This could be attributed to the reduced amount of observations of these three satellites. C28 also showed large clock differences, which may have been because the clock of this satellite was under-testing during the test period. \begin{table}
\begin{tabular}{l c c c c c c} \hline  & **COD** & **ESM** & **GFZ** & **GRG** & **SHA** & **WUM** \\ \hline COD & - & 0.09 & 0.24 & 0.08 & 0.51 & 0.09 \\ ESM & - & 0.25 & 0.10 & 0.50 & 0.12 \\ GFZ & & - & 0.25 & 0.54 & 0.24 \\ GRG & & & - & 0.51 & 0.10 \\ SHA & & & & - & 0.51 \\ WUM & & & & & - \\ \hline \end{tabular}
\end{table} 
Table 6: Mean STD of Galileo clock differences among different ACs (units: ns).