where, at time formula_3, formula_4 is the plant's state; formula_5 is its inputs; and formula_6 is its outputs. These equations simply say that the plant's current outputs and its future state are both determined solely by its current states and the current inputs. (Although these equations are expressed in terms of discrete time steps, very similar equations hold for continuous systems). If this system is observable then the output of the plant, formula_6, can be used to steer the state of the state observer.