The most reliable way to determine VCMM capability for your application is to measure your actual parts. The mechanical accuracy of most CMMs and VCMMs has improved during the last 15 years while the prices have dropped. The software error-compensated machines actually hold their calibration over time better than do machines designed for mechanical adjustment. These tend to lose their calibration due to being moved, structural stresses caused by machine operation and external vibration. It's the random and application-dependent errors that aren't yet as well accounted for.
Most edges typically have a radius or corner break for safety reasons.
When these edges are illuminated, a bright band of light reflects back that is actually offset from the real edge. Surface Illumination of an Electronic Part images are of the same stamped electronic part. The part, stage and graphical tool haven't moved, but the measurable edge as seen with surface illumination is clearly offset from the actual edge. The graphical icon in the images is a video micrometer that allows the magnitude of this effect to be quantified. The contamination wasn't visible with the naked eye.