... The following table aims to provide a guide to the unreddened colours expected for main sequence stars of spectral types B0 to M4. The data are taken from Fitzgerald (1970 - A 4, 234), who provides UBV data for spectral classes O5 to M8, and from Ducati et al. ... 0.12 . ... The following table gives the mean colour/spectral type relations derived from these observations: . ... 0.005 . ... Based on that dataset, they have compiled mean relations between spectral type and the Sloan colours. ...