I guess the question is not to debug the udf, but rather to ask, if I have missed out on any formula that calculates the surface integral?nI already have the link that you provided in my equation, (see second last line within comments), so I am already summing the total pressure, multiplying with an area, summing this product, and dividing with total area.nOr perhaps a way to narrow down the source of this difference would also be helpful.n