For vector flux, the surface integral of j over a surface S, gives the proper flowing per unit of time through the surface: d q d t = ∬ ∬ S j ⋅ ⋅ n ^ ^ d A = ∬ ∬ S j ⋅ ⋅ d A , where A (and its infinitesimal) is the vector area – combination A = A n ^ ^ of the magnitude of the area A through which the property passes and a unit vector n ^ ^ normal to the area. Unlike in the second set of equations, the surface here need not be flat.