Temperature sequence for moderately luminous supergiants of mid B-types. At constant luminosity, the main criterion is the ratio of Si II 4129 Å to He I 4144 Å, whose progression is clear here. The difference between the B6 Iab and the B7 Iab stars is, however, very small, and the secondary criterion Mg II 4481 Å to He I 4471 Å would not allow a separation between them. Note that 13 Cep (HD 208501) was a B8 Ib standard, but the width of its Balmer lines suggests higher luminosity, and it fits nicely in the sequence with this new classification.