The luminosities of the Beta Canis Majoris variables, the zero age main sequence and the distance of the Sco-Cen association.

The Hy-luminosity calibration of Balona & Crampton is used to derive the zero age main sequence. This is about 0m.2 brighter than Blaauw's. The H7 calibration is applied to the CMa variables. The results are consistent with a theoretical P-L-C relation. The pulsation constant, Q, is implying that the variables pulsate in the first overtone. The variables fall in the S-bend region of evolution. Contrary to previous work the slope of the instability strip is not inclined to the S-bend locus in the Te diagram. The calibration is consistent with the interferometric absolute magnitude of o' Vir and the astrometric distances of CMa stars in Sco-Cen. It is brighter by 0m.3 than the absolute magnitude calibration of Jones & Shobbrook. There is a serious discrepancy between the mean astrometric distance modulus of Sco-Cen (Sm.78) and the H7 modulus (6rn.46). It seems possible that the cut-off applied to eliminate poor proper motions may have significantly biased the astrometric distance. A difference of 0m.24 in the modulus of Sco-Cen derived from H7 and from the index may be partly due to inclusion of a temperature term in the Hy calibration but not in the calibration.