Differences in logarithmic abundances between the three stellar groups and M 67-1194 for the chemical elements analysed. A systematic difference between the SG and TO stars is apparent and the mean value for the MS stars falls in between the other two groups. Arrows indicate model predictions by O. Richard (priv. comm.) of the effects of atomic diffusion (with gravitational settling and radiative levitation) on the surface abundances when moving from TO stars to SG stars in the temperature regime covered in this study.