Hi, I've not looked in detail, but for your calculation, it looks to me that you don't need an integral quantity. Just use a postprocessing : { Name Tave; Value { Integral { [ what you want ] ; In Sfc ; Integration I ; Jacobian J ; }}} and then in PostOperation : Print[ Tave [Sfc], OnGlobal , File "surf.result", Format Table]; (tell me if I'm wrong) Regards, O.C.