So the number basically describes its position along that sequence, along the polypeptide sequence. So all these six residues contain positive charges and those positive charges form these electrostatic interactions with the negative charges on the two three BPG. And this decreases the overall net charge in this area and that stabilizes the deoxy hemoglobin and it stabilizes the T state. And by stabilizing the T state, that drives the equilibrium back towards the T state. And now the T state can exist by itself without binding to that oxygen. And what that means is that basically shifts the entire curve toward the right side and then decreases the affinity of the hemoglobin for oxygen because now the T state can exist because it is more stable than in the absence of that 23 BPG.