  We demonstrate that the sequence of distorted commensurate phases observed in
tilted chiral smectics is explained by the gain in electrostatic energy due to
the lock-in of the unit cell to a number of layers which is the integer closest
to the ratio pitch over thickness of the subjacent Sm-C$^*_\alpha$ phase. We
also explain the sign change of the helicity in the middle of the sequence by a
balance between two twist sources one intrinsic and another due to the
distortion of the Sm-C$^*_\alpha$.
