Average Fourier Shell Correlation (avgFSC) between model and observed structure factors for reflections not included in refinement. The average FSC is a measure of the agreement between observed and calculated structure factors. sum(N_i FSC_free-i) avgFSC_free = --------------------- sum(N_i) N_i = the number of free reflections in the resolution shell i FSC_free-i = FSC for free reflections in the i-th resolution shell calculated as: (sum(|F_o| |F_c| fom cos(phi_c-phi_o))) FSC_free-i = ------------------------------------------- (sum(|F_o|²) (sum(|F_c|²)))^1/2 |F_o| = amplitude of observed structure factor |F_c| = amplitude of calculated structure factor phi_o = phase of observed structure factor phi_c = phase of calculated structure factor fom = figure of merit of the experimental phases. Summation of FSC_free-i is carried over all free reflections in the resolution shell. Summation of avgFSC_free is carried over all resolution shells. Ref: Rosenthal P.B., Henderson R. "Optimal determination of particle orientation, absolute hand, and contrast loss in single-particle electron cryomicroscopy. Journal of Molecular Biology. 2003;333(4):721-745, equation (A6).