Room-temperature thermoelectric power S^290 as a function of hole concentration per planer Cu atom (P_pl) has been studied in a chain-free double-layer Y_1−_xCa_xBa_2Cu_3O_6. S^290(P_pl) of Y_1−_xCa_xBa_2Cu_3O_6 (P_pl=x/2) behaves identically to that of single-layer La_2−_xSr_xCuO_4 (P_pl=x). In order to show the validity of the present scale of S^290(P_pl), we demonstrate the phase diagram for bilayer Yba_2Cu_3O_y system and Bi_2Sr_2CaCu_2O_y system and discuss.
