Various A_n(T_n) relations. Numbers in brackets above the lines correspond to the row numbers in Table 3. The solid lines (2) and (5) correspond respectively to the “lower and upper limits” (see text) deduced from the theoretical relation for solar-aboundance discs with α_h = 0.2 (C₁ = −0.95   and   1.2). Helium disc theoretical relations are represented by the dotted lines (4) and (6) (C₁ = 0.1   and   1.3). Solid lines 1 and 3 illustrate the α_h dependence of the A_n(T_n) relation: for the same binary parameters, they correspond to α_h = 0.01 and α_h = 0.2, respectively. The upper and lower uncertainty of observational K-P relation fitted to the systems are marked with thick, dashed lines. The sample of binaries marked on the plot consists of U Gem-type systems listed in Table 1 (full circles and asteriks), AM CVn systems: PTF1J0719, CR Boo and V803 Cen (both in cycling state outbursts) (open circles) and SU UMa stars (normal outbursts only, full squares) from Ak et al. (2002) and updated Cataclysmic Binaries Catalog (Ritter & Kolb 2003).