Accuracy assessment of the block–wise recursion compared to the component-wise recursion (Andersen’s method [7]) for calculating Zernike basis functions: (a) 120 test positions from a circular region with five radii (1.00, 0.96, 0.88, 0.72, 0.40) and 24 uniformly distributed azimuth angles; (b) 120 difference curves (color–coded) with respect to the polynomial orders, each curve representing the maximum absolute differences between two sets of Zernike components along the orders from 0 to 99 for a position in (a); (c) the logarithmic representation (log10) of the corresponding curves in (b), of which 17 curves are distinguished from the others by their difference value of over 3 × 10⁻¹⁵ and whose corresponding positions all lie on the unit circle.