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. If we find the corresponding y value for the black curve, the pure hemoglobin, the value is around 0.9. And that means 90% of the hemoglobin, the pure hemoglobin will be saturated with oxygen. And so that means a difference of 98 -90.