Uncertainties on EW or pEW. In the top panel, we show the distribution of the uncertainties for Giraffe (red hatched histogram) and UVES (blue hatched histogram). In the bottom panel, we plot the uncertainties on EW or pEW as a function of the S/N. Colours are the same as the top panel, and the plot was limited to S/N < 400 for better clarity. Uncertainties are higher for stars with higher rotational velocity.