Measured iron abundance vs. stellar parameters as derived in Romaniello et al. (2008, see their Table 9), together with the results of a linear regression (red lines). A clear residual trend is present with v_turb, which is responsible for the large scatter of σ = 0.13 that our analysis does not confirm. The points are colour-coded according to the phase along the pulsational cycle within which the stars were observed, with the scale represented by the bar on the far right.