And what that means is 21% of that oxygen of that hemoglobin has successfully unloaded and released the oxygen to the resting cells of our body. So this is how much oxygen can be unloaded by the hemoglobin when it goes from the lungs to the resting tissue. Now, what about if we're exercising? How much can hemoglobin deliver if our tissues are exercising? Well, in the case of the exercising tissue, the partial pressure is at 20 mercury. And we see that because we have this sigmoidal shape curve, there is a drastic drop in our fractional saturation of hemoglobin.