\begin{table}%t1
\caption{\label{tab:calib} Experimental protocol including photometric and  interferometric measurements.}
\small%\centerline
 {
\begin{tabular}{cccccc}
\hline \hline
Step & Sh1 & Sh2 & Sh3 & Sh4 & Measurement\\
\hline
1 & X & X & X & X & B$_{\rm g}$\\
2 & O & X & X & X & $P_{1}$\\
3 & X & O & X & X & $P_{2}$\\
4 & X & X & O & X & $P_{3}$\\
5 & X & X & X & O & $P_{4}$\\
6 & O & O & O & O & $I$\\
\hline
\end{tabular}}
\medskip
Sh = shutter; O = open; X = closed.
\end{table}