However, the association constant for the addition of monomer units at the barbed end has been measured to be more favorable. This contradiction can be rationalized qualitatively by noting that the behavior of a system in a non-equilibrium steady state is controlled by kinetic considerations; although the association constants (i.e., the ratio of on/off rate constants) at the barbed and pointed ends must be the same, the rate constants themselves can differ. Similarly, the overall rate of ATP-actin hydrolysis and monomer dissociation (k+1) at the barbed and pointed ends need not be identical. Indeed, the hydrolysis process itself is actually quite complicated (see below). The conclusion is that, regardless of the finer details, the apparent difference in experimentally determined association constants for ATP-actin to the pointed and barbed ends of an actin filament arises due to kinetic differences in processes taking place.