Summary of the cryoEM 3D classification and refinement scheme for FluB polymerase complexes. Initially, ~ 615k particles were classified into eight 3D classes with angular assignment (upper lane, number of particles in each class is indicated in thousands). Incomplete, low resolution, and damaged particle classes were excluded from further data analysis. The four most prominent 3D classes of the complete FluB polymerase were merged into a global consensus model (second line) and further classified into six classes (third line). Atomic resolution cryoEM maps for pre-initiation and elongation states were refined and post-processed with their respective masks in RELION (bottom line right) and amplitude scaled in LocScale (bottom line left).