The shape of the action potential calculated with the Hodgkin-Huxley equations matches experimental records rather well except for a marked deviation in the falling phase. Cole refers to this deviation as the "gratuitous bump." The figure below showing the bump is a reproduction of Figure 3.47 from Cole's book Membranes Ions, and Impulses. SEAC refers to the computer of the National Bureau of Standards used to make the first automatic calculation of the action potential.