Uncertainty on mass in transit follow-up vs. spectral type for two planet masses (1 M_Earth on left hand-side and 2 M_Earth on right hand-side), for PHZ_med, and for different values of N_obs: 180 points (yellow), 1266 points (brown), and 2352 points (pink). The 1σ levels are shown as solid lines, the 2σ levels as dashed lines, and the 3σ levels as dotted lines. The black horizontal line shows the 20% level for reference. The 2-σ and 3-σ uncertainties are in some cases out of scale for clarity.