Filtering.- A Brief History of Filtering.- Filtering in the Frequency Domain.- Filtering in the Time Domain.- Gaussian Filter.- The 2RC Filter.- Filtering Roundness Profiles.- Filtering 3D Surfaces.- Advanced Filtering.- Gaussian Regression Filters.- Spline Filter.- Robust Filters.- Envelope and Morphological Filters.- Multi-scale Filtering.- Fitting.- to Fitting Substitute Geometry.- Least-Squares Best-Fit Line and Plane.- Non-linear Least-Squares I: Introduction.- Non-linear Least-Squares II: Circle, Sphere, and Cylinder.- Fitting Radius-Suppressed Circle Data.- Exchange Algorithms for Minimum Zone.- Reference Circle-Fitting Using Linear Programming Simplex.- Parameterization.- Surface Finish Parameters I: Amplitude, Spacing, Hybrid, and Shape.- Surface Finish Parameters II: Autocorrelation, Power Spectral Density, Bearing Area.- 3D Surface Texture Parameters.- Errors and Uncertainty.- Uncertainty Considerations.- Uncertainty Propagation in Computations.- Error Separation Techniques in Roundness Metrology.- Other Relevant Topics.