So this red curve describes the oxygen dissociation curve for hemoglobin. So as we go from right to left, from the lungs to our tissue, our hemoglobin essentially unloads and releases that oxygen. So let's begin inside our lungs. And let's suppose we're going from the lungs to our resting tissue. So the lungs have a partial pressure of 100 mercury, and the corresponding Y value at this point is about zero 98. So that means about 98% of the hemoglobin is fully saturated inside our lungs.