So let's begin inside the lungs. So, inside the lungs, the partial pressure is about 100 mercury, and so the x value is 100. And if we find the corresponding y value on these two curves, we get the same value of about zero point 98. So inside the lungs, 98% of these two types of hemoglobin, the pure hemoglobin and the hemoglobin found in red blood cells, 98% of that hemoglobin is saturated with oxygen. Now, what happens when we go down to our exercising tissues where the partial pressure drops to about 20 mercury? So, here is where we see that tremendous difference.