Stability against S/N per Å for three relations of different maximum FR excursion (cf., color coding and legend in the lower panel). The corresponding S/N per resolution element for four different resolving powers (see legend) are given in the top panel. Shown are the measured mean values (colored dashed lines) and 1 σ standard deviations (solid lines enclosing filled areas) from an MC simulation with artificially injected noise (see main text for details). The zoom-in view emphasizes the (marginal) relation-to-relation inaccuracies (see middle panel of Fig. 10). Vertical lines indicate the minimum S/N requirements for different 4MOST consortium surveys: S∕N = 50 Å⁻¹ in the magnesium or calcium triplet regions (4MIDABLE-LR¹⁰); S∕N = 30 Å⁻¹ in the magnesium or calcium triplet regions (1001MC¹¹, LR); S∕N = 100 Å⁻¹ at 6200 Å (1001MC, HR; 4MIDABLE-HR¹²).