a) Effective temperatures for MK luminosity classes V, IV, and III determined by de Jager & Nieuwenhuijzen (1987) against those extracted from the BCD calibration; b) effective temperatures determined from the uvby photometry using the calibration by Napiwotzki et al. (1993) against those obtained in the BCD system; and c) average effective temperatures determined by Adelman et al. (2002), Nieva (2013), and Fitzpatrick & Massa (2005) against those obtained in the BCD system for a number of common OB stars without emission. The red dashed lines correspond to x = y diagonal.