We discuss the fundamental principle and application of estimating ±π/2 type of phase using ∑ relationship in noncentrosymmetrical crystal structures. We obtain an optimum coincident principle between specifying the origin of unit cell, enantiom-orph and estimating ±π/2 type of phase. A group of phases of this type is estimated by ∑7,∑3 relationships for two known crystal structures in terms of the above mentioned principle. The results are satisfactory.