Phase refinement by δP recycling. (Top) Initial (or updated) phase estimates are used to compute δP; (middle) δP values are compared with Δ = 2.5σP to impose positivity, thus leading to the constrained δP,Δ; (bottom) new structure-factor estimates are obtained by Fourier transforming δP,Δ. CC measures the correlation between observed and new amplitudes. Refinement continues until convergence is reached. This algorithm is also valid for δM, the principal difference being substitution of E2 − 〈E2〉 by E − 〈E〉.