Normalised mode inertias as a function of averaged periods spacings (defined as π_n = (1 /ν_{n − 1} − 1 /ν_{n + 1}) / 2, where n is the radial order). The lower panel corresponds to Model 1 with a 90% decrease in density near the surface, whereas the upper panel uses Model 1 with KBCD surface corrections, adjusted so as to match (as best as possible) the frequencies of the modified model. The increased scatter at low inertias in the upper panel illustrates the mismatch between period spacings and mode inertias.