Priam estimates of A_G and E(BP − RP) for red clump stars from Bovy et al. (2014). Note that G + 5log₁₀ϖ + 5 (= M_G + A_G) is an observable. The horizontal dashed lines show M_G = 0.51 mag for A_G = 0 and G_BP − G_RP = 1.23 mag for E(BP − RP) = 0, which are the approximate absolute magnitude and intrinsic colour of the red clump. The diagonal line is not a fit but the locus of constant absolute magnitude where we expect extincted red clump stars to lie. Panels a and c: all red clump stars, colour-coded by relative parallax uncertainty. Panels b and d: red clump stars with parallaxes uncertainties better than 20%, colour-coded by metallicity estimates from APOGEE (Alam et al. 2015).