This video shows how to measure radius of curvature using 4D Technology 4D InSpec Surface Gauge. Measure small and medium radii, and measure blend radius at multiple locations and directions.
UPDATE (July 2019): To make this measurement best, it’s best not to include any portion of the flat adjacent to a radius (as is the case in this video). Including a corner and a portion of a flat will produce an inaccurate radius calculation.
To avoid including a corner, simply click and drag over your area of interest (radius segment) in the 2D graph. This will highlight an area in green, and the Radius of Curvature will be calculated only for that section.