For divergance thereom, say i have a volume integral to calculate of form [tex] \iiint_V \nabla F dV [/tex] i can relate it to the form: [tex] \iint_S F.dS = \iiint_V \nabla F dV [/tex] and calculate using the left hand side, [tex] \iint_S F.n dS [/tex] where n is the unit vector normal to the surface of integration. for my surface I have a cylinder. of form x^2 + y^2 =< 1 for 0 =< z =< 3 So splitting this up brings me 3 surfaces, the top 'cap' the bottom 'cap' and the part around the middle. i can compute by intergrating the vector field seperately over each surface (i think) and summing over each suurface. question is do i use the same normal vector for all surfaces ie the normal to the main surfaces, or do i for each seperate surface use a different normal vector? i switched to cylnderical co-ords to solve this. i assumed at first it was a seperate normal for each vector. but this gave me a dot product of zero for the area of the strip aroundthe cylinder.