It binds that oxygen strongly. And that's why we have this sharp increase in that curve immediately after we begin increasing the concentration of that oxygen. So we see that at a partial pressure of 2 million meter of mercury. So let's take our marker out. So, at this quantity here, which is about 2 million meter of mercury, if we basically draw a straight vertical line and eventually we hit the curve, we hit the curve at this value. And this value describes a value of 0.5 fractional saturation of protein.