So, this is just to kind of end the wave slope concept that we basically have something called wave slope and it it will have a phase gap with respect to wave, actually if you can see when the peak of this occurs here, the peak of this occurs other way round we can see, the this peak is occurring here, where this peak is occurring here. So, again one can see, the phase gap between the two for example, there is a motion that follows this and a motion that follows this we would know that they actually do not occur maximum the same time; when the maximum of this occur this is 0. So, with that this is about wave slope, now I will come to definition of ship motion.