compute msd result

Dear all:

I am trying to use compute msd and the manul says the calculation results is:

The 4th element is the total squared displacement, i.e. (dxdx + dydy + dz*dz)

I am wondering this dx dy dz each step are for the Xi and the X0. Or it means Xi and X(i-1).

Sincerely yours

Peiyu