Error ellipses computed as the difference between the input and the derived parameters of our pipeline, for the set of 2000 spectra of Sect. 3, with SNR  ~  10. These figures illustrate the extent of the correlation of the uncertainties in our parameter derivations. The 2-dimensional histograms have been obtained by binning by 16 K in effective temperature, 0.025 dex in log g and 0.016 dex in [M/H]. The isocontours are for 2, 5, 15 and 30 stars.