Mathias,rnrnThank you again for your patience.rnrnI think you and I are missing an important point…rnrnblock.get(iX,iY).computeRho() computes the fluid’s actual RHO not (RHO + 1).rnrnUsing the actual RHO for the fluid, your computed pressure is (I think incorrectly)…rnrnP = (RHO – 1) * (Cs*Cs)rnrnI don’t think this is what you want.rnrnRegards,rnRandyrn