Published online by Cambridge University Press: 14 August 2015
It is shown that a large scatter exists in all color-color and color-spectral type diagrams. This scatter can not be neglected and its importance is shown in several examples. A new approach is then developed for the study of the precision attainable in spectral classification. It is found that for A-type stars MK classification is about as accurate as photometry, whereas for B-type dwarfs photometry is at least two times more precise than MK classification. A precision of ±0.6 tenths of a spectral class seems attainable in both groups.