Global seismic parameters for NGC 6791 and NGC 6819, where the RGB stars are indicated by green circles and red triangles, respectively, and the RC stars of both clusters by blue symbols. Grey-filled squares show the EBs from Sect. 2. Panel a: ratio of Δν_c and ν_max; panel b: the phase shift ϵ_c of the central radial mode. The vertical dashed lines indicate the median large separations of RC stars in the two clusters. Panel c: curvature term α. Panel d: ratio of Δν_cor computed in different ways (Eqs. (4) and (6)); panel e: ratio of central large separation and Δν_cor computed according to Eq. (4). The dashed lines in panels c, d, and e indicate the scaled curvature term from Mosser et al. (2013) and unity, respectively.