But when we have two three BPG present, the red curve is the curve that describes the relationship between our hemoglobin and the partial pressure of oxygen. And notice that the red curve is shifted to the right of our blue curve. And that's exactly what we mean by shifting the curve to the right side. Now, why does this actually take place? Well, let's take a look at our tissue partial pressure of 40 mercury. So if we draw a vertical line and we find the corresponding Y coordinates, the Y points for the blue curve, when we don't have any two three BPG present in the red blood cells found inside the capillaries, we see that we have a percent equaling to about 70% saturation of hemoglobin.