Now, this continues to take place until we reach about zero millivolts. When we reach about zero millivolts, the rate of movement of our sodium, of the potassium to the outside is equal to the rate of movement of the calcium inside. And what that basically means, because our rates are equal, because we have the positively charged potassium leaving the cell, but we have the positively charged calcium entering the cell, and the rates are equal. That means the charge on the membrane will basically be the same for a short period of time. And this is shown by the phase number two, the blue region. So once the cell reaches a voltage difference of about zero millivolts, the rate of influx of the calcium is equal to the rate of e flux.