 In some cases, it might be useful to describe the pressure difference caused by a number of fluids. You would step through these with individual power equations. We could figure out the pressure difference between the atmospheric pressure and the interface between fluid 1 and figure 2. We could figure out the pressure difference between atmospheric pressure and the pressure at the interface between fluid 1 and fluid 2 by using the density of fluid 1 times gravity times h1. And then we could figure out the pressure difference between fluid 1 and fluid 2 and fluid 2 and fluid 3 by using the density of fluid 2 times gravity times h2. By stepping one fluid at a time, you can work your way from atmospheric pressure all the way down. Let's try an example of that.