Qualitative teaching aid — goals map to family-appropriate methods, and tiers are a planning vocabulary, not measured roughness; actual results vary with machine, material, parameters, orientation, and geometry. A reflective surface does not by itself establish dimensional accuracy, flatness, or fit — those needs call for machining, grinding, lapping, inspection, and stock allowance. Specify finish by face and verify on standardized artefacts or project coupons with your provider.