I went to visit the space center in my new home of Huntsville AL the other day. I figured i'd do a quick calculation from tank capacity as read from the plaque for the second and third liquid hytrogen stages. Assuming an ideal reaction, there should be a mass ratio of oxyogen to hydrogen of 4:1. This calculation comes from the straight foreward chemistry of the reaction and the respective molar masses of hydrogen and oxygen. The third stage was close to this ratio. However, the second stage was closer to 5:1. Could a difference this big be atribuable to the enginering of a particular geometry of the tank to fit within the structure?