Figure 19(b) shows the dependence of the fraction of non-bridging oxygen atoms f_{NBO} on the Al-O coordination number for the tectosilicate glasses with f_{NBO} ~0 at rho^prime = 1. The fraction of NBO atoms was calculated by assuming that f_{Si(IV)} = 1 and only the Si(IV), Al(IV) and Al(V) species contribute towards the network.