Null depth measured in four narrowband filters using the reflexive chessboard phase mask (short segments of line). The curves give the theoretical null depth of a perfect component. The red color refers to a null depth based on a non-nulling reference produced by a flattened chessboard; the blue color refers to a reference produced by adding a λ_o/2 opd to one pupil of the chessboard: it measures a star-to-planet contrast ratio than a null depth (see text). The dotted line gives the nulling depth for a perfect Bracewell interferometer.