Which one of these is not a type of continuity in the Studio Spline command?

The correct understanding of continuity in the context of the Studio Spline command in Siemens NX involves recognizing the various degrees of geometric relationships between curves.

G1 continuity, referred to as tangent continuity, ensures that two spline curves meet at a point with the same tangent direction, allowing for a smooth transition without abrupt angles. G2 continuity, known as curvature continuity, goes a step further to ensure that the curves not only connect tangentially but also have the same curvature at the point of intersection, offering a visually smoother flow.

G3 continuity, or flow continuity, is one that is often less discussed in common spline operations compared to G1 and G2, but it extends further to manage how the curvature of the spline transitions, thus allowing an even more fluid connection between curves.

G4 continuity is not a standard term recognized in the context of spline continuity types. While there may be advanced theoretical applications or interpretations that suggest it, it is not one of the standard measures like G1, G2, or G3, which are well established in spline design. Thus, identifying G4 as not being a recognized type of continuity in the Studio Spline command is correct.