Velocity lower bound and upper bound together with the classification level of significance 100(1 − α)%. The red, blue, and green (solid line) curves indicate a supersonic, sonic, and subsonic classification (left ordinate axes), respectively at a 50% level of significance. The dotted line curves show the level of significance (rights ordinate axes). The horizontal dashed line represents the background sound speed. These flows all have a majority supersonic classification.