Period spacing of the l = 1 mixed modes ΔΠ₁ (expressed in seconds) as a function of the large frequency separation Δν (expressed in μHz). The period spacing is measured for 3388 stars out of the sample of 4465 RGs. The colors of the markers indicate the stellar masses as indicated in the colorbar (deep blue is less that 1.5 M_⊙). The dashed line separates the red clump stars (above) and the RGBs (below).