Now, if we begin to exercise, if our tissues are exercising, then what happens is the pressure, the partial pressure inside the tissue, drops even more. So let's say now it drops to 20 mercury. Now, because of this sigmoidal curve, we have a very steep slope. And what that means is a very small change in partial pressure will cause almost all of that hemoglobin to fully unload its oxygen. And that will ensure that all the oxygen is readily delivered to the exercising and active tissue. So on this side of the curve we see that a small drop in pressure will basically unload most of that oxygen.