Wafer package:nlme R Documentation _M_o_d_e_l_i_n_g _o_f _A_n_a_l_o_g _M_O_S _C_i_r_c_u_i_t_s _D_e_s_c_r_i_p_t_i_o_n: The 'Wafer' data frame has 400 rows and 4 columns. _F_o_r_m_a_t: This data frame contains the following columns: _W_a_f_e_r a factor with levels '1' '2' '3' '4' '5' '6' '7' '8' '9' '10' _S_i_t_e a factor with levels '1' '2' '3' '4' '5' '6' '7' '8' _v_o_l_t_a_g_e a numeric vector _c_u_r_r_e_n_t a numeric vector _S_o_u_r_c_e: Pinheiro, J. C. and Bates, D. M. (2000), _Mixed-Effects Models in S and S-PLUS_, Springer, New York.