Hi akoutras,nThank you very much for your comment and the book reference! Now I understand that those two methods are actually the same central difference method. However, I have to still study the book more carefully and maybe I'll understand this better after that. nI find it interesting why does DYNAmore website say that the difference formula for velocity is not central difference even though it's actually presented just the same way as in central difference method:nnI'm also still unsure if LS-Dyna actually uses x or u, since DYNAmore says that x is used in the central difference method and Theory Manual that u is solved by the central difference method, after which it is stored and then used for calculating x. nMaybe it's the way as stated in the actual theory manual by LSTC since they also say that it's beneficial in order to reduce round-off error? I'm not quite sure though, how does using the displacements u reduce the round-off error instead of directly solving the coordinates x. nBest regards,nNiklasnn