Star formation evolution (solid curve) and (1 /T_spin)(d_abs/d_QSO)² (error bars, scaled by a factor of 450, Sect. 3.2) superimposed upon the ratio of angular diameter distances for various QSO redshifts (broken curves). These are shown for z_QSO = 1,2,...,8 where the QSO redshift is given by the terminating value of the curve showing the absorption redshift distribution of (DA_abs/DA_QSO)².