Now, what we are saying is, if this is the position of the propeller disc, how will the pressure change. Pressure we said here would be P 0 let us say at far forward of the propeller and it is dropping to a value, negative value just before the disc where it has a increase in pressure, certain increase in pressure due to propeller action, and then, this increase in pressure will reduce further to the same value P 0. We can call this pressure P 1 and this pressure P 1 dash, that is, before the propeller disc, the pressure was P 1, and the after the propeller disc, the pressure is P 1 dash. Is that clear?