Well, recall that at 100 mercury that is the partial pressure of our alveoli within the lungs. But at a partial pressure of 40 mercury, this is the partial pressure within our tissue. Notice what the red curve tells us. It tells us that at a higher temperature given by the red curve, if we look at the value for the Y axis this gives us a percentage of about 60% saturation. But the blue curve describes a percentage that is equal to about 70. So the red curve describes hemoglobin that is less likely to bind to oxygen and more likely to unload and release that oxygen to the exercising tissue.