Now, I have already told you that the pressures for a far forward and far aft will be same as, as, the static pressure. So, what we have here - P 0 equal to P 2. Now, what are the assumption we have made so far or what we are going to make as we along to find the efficiency of a Propeller based on this principle? We have made some very drastic assumptions. One assumptions we have already mentioned that there is a change in pressure and we do not know how it is.