Root-mean-square deviation of the FEM φ_⊥FEM and new φ_⊥C look-up tables. The rms value for each case only contains the 96 actuator positions and not the entire computed phase-error map. Upper plot shows the difference from both methods. Most of the corrected deviation happens at lower elevations, where the random-surface-error efficiency dominates (see Fig. 10). The horizontal line corresponds to the traditionally defined value for a good efficiency, δ_rms ≤ λ/16 (ε_rs = 0.54), and it has been drawn only as an indicator.