\begin{table}%t2
%\centering
\par
\caption {\label{tabres2}Accuracy $\delta M /M$ on mass determination, for a frequency accuracy of 0.2 $\mu$Hz, obtained from different methods of evaluating spectra difference and for different values of considered modes.} 
%taken into account.}
\begin{tabular}{cccc} 
\hline\hline
Nf of modes  & 20 & 40 & 60 \\
\hline
 $\delta M /M$  with $\delta \nu$ & 0.02 & 0.01 & $<$0.01\\
$\delta M /M$  with $\delta_{\rm sls}$ & $>$0.07 & 0.02 & 0.01\\
\hline
\end{tabular}
 \end{table}