Kiel diagram colour-coded with the lowest lead abundance (in dex) that could be detected in a spectrum whose (normalised) Pb line core flux is 0.5% deeper than that of a reference spectrum with [Pb/Fe] = −2.0 dex (i.e. negligible amount of Pb, and therefore undetectable line). For each combination of effective temperature and surface gravity, we estimated this lowest Pb abundance for three values of [M/H]: 0.0, −0.5, and −1.0 dex (from top to bottom and left to right in each small square).