16:16 If delw.V is zero because w is constant on a curve on the same level surface .. then delw . any other vector would be zero be it tangent or not .. because del w is always gonna be zero on the level surface.. isn't it ?####[['delw.V', 'Course_General_Feedback', 'NEU'], ['zero', 'Course_General_Feedback', 'NEU'], ['w', 'Course_General_Feedback', 'NEU']]