The y axis is basically the CO2 content in the blood, dissolved in the blood. And the x axis is the partial pressure of the carbon dioxide in that region in the blood. Now this relatively straight line, the black curve, basically describes how much carbon dioxide we can fit, we can dissolve inside the blood at some given partial pressure of carbon dioxide. And notice as we decrease the concentration of oxygen inside the red blood cell, the Halden effect basically causes a leftward shift in this curve. And so the curve moves into the blue position. Now why is that?