Line-strength differences between versions 9.0 and 9.1 of stars in the MILES stellar library. The solid line marks the zero level. The dashed and dotted lines indicate the expected uncertainty for spectra with a signal-to-noise ratio of 30 and 75 Å^-1 respectively (see Cardiel et al. 1998). The vertical axis has been adjusted to twice the maximum uncertainty expected for a spectrum with a signal-to-noise ratio of 30 Å^-1 within the line-strength index range shown.