Final state interaction accounts for the large $SU(3)_f$ violations in the non leptonic decays of the charmed pseudoscalar mesons into two light pseudoscalars .

This gives information for the phases of the amplitudes proportional to $\sin{(\theta)_C}$ and on the CP violating asymmetries, which depend on two parameters in the framework of the standard model.

To agree with the present experimental infomation one needs a large value of the parameter, which is expected to be small as a consequence of the Zweig selection rule, which would imply smaller values for the three more recent measurements of the CP violating asymmetries at $LHC_b$.