i think there is a mistake in the slide where it says that the plot of P vs log of t after the end of the pressure transient ends is a straight line but as is clear from the equation of PSS that the plot is first of all between P and t and that too is linear so bit of a correction here. Although the statement is in line with the thought that the plot of P vs log of t is linear but that is in the Transient state not in the PSS region.