\begin{table} \par \caption{\label{tab:datasets}Characterization of the different datasets used in the fit. } %\centerline {\small \begin{tabular}{ l r r r r r r } \hline \hline Source$^a$ & \# of Transitions$^b$ & Max. $J$ & Max $K_{\rm a}$ & \multicolumn{2}{c}{Frequency [GHz]} & $\sigma$ \\ & & & & \multicolumn{1}{ p{3em} }{\raggedleft Min.} & Max. & \\ \hline Synthesizer (Cologne) & 344 (259) & 54 & 19 & 39 & 56 & 1.02 \\ BWO (Cologne) & 586 (273) & 70 & 27 & 69 & 897 & 0.90 \\ BWO + SL (Cologne) & 1663 (635) & 63 & 27 & 263 & 2099 & 0.95 \\ Multiplier chain (JPL) & 2234 (435) & 67 & 30 & 780 & 1665 & 1.08 \\ \hline \citet{Niide2003} & 16 ( 13) & 7 & 2 & 12 & 25 & 1.77 \\ \citet{Durig1976} & 20 ( 15) & 4 & 1 & 29 & 36 & 0.50 \\ \citet{Lovas1979} & 191 (157) & 22 & 6 & 9 & 112 & 0.74 \\ \citet{Neustock1990} & 79 ( 66) & 24 & 5 & 63 & 222 & 0.96 \\ \citet{Groner1998} (Klystron) & 962 (702) & 25 & 6 & 94 & 544 & 1.08 \\ \citet{Groner1998} (FASSST) & 735 (386) & 49 & 10 & 263 & 340 & 0.85 \\ \hline % \end{tabular}} \par \medskip $^a$ The first four rows summarize transitions measured within this work.\\ $^b$ The number of assigned transitions is given followed by the number of different frequencies in parentheses. The last column shows the unitless standard deviation of the dataset in the fit. \end{table}