Comparison between velocity measurements for stars observed in two Giraffe setups. Upper panels: we show the distribution of velocity differences with respect to the velocity measured with HR 10 for all the stars observed (from left to right, with HR 21, HR 11 and HR 13) and estimated uncertainties on V_r ≤ 1 km s^-1 for each measurement. The mean difference and the rms dispersion are also shown. Bottom panels: as above, but now the velocity difference is normalised by the predicted uncertainty. It can be appreciated that the measured uncertainty in the velocity distribution is very close to the unit variance Gaussian (standard deviation =0.88, 1.59, and 0.97 for HR 21, HR 11, and HR 13, respectively).