diff --git a/example.conf b/example.conf
index 58fc969..2ebaeac 100644
--- a/example.conf
+++ b/example.conf
@@ -4,7 +4,7 @@ GridRes      = 128
 # length of the box in Mpc/h
 BoxLength    = 250
 # starting redshift
-zstart       = 49.0
+zstart       = 100.0
 # order of the LPT to be used (1,2 or 3)
 LPTorder     = 3
 # also do baryon ICs?
@@ -15,8 +15,9 @@ DoFixing     = no
 ParticleLoad = sc
 
 [cosmology]
-#transfer     = CLASS 
-transfer     = eisenstein
+transfer     = CLASS
+ztarget      = 100.0 
+#transfer     = eisenstein
 Omega_m      = 0.302
 Omega_b      = 0.045
 Omega_L      = 0.698
diff --git a/src/plugins/transfer_CLASS.cc b/src/plugins/transfer_CLASS.cc
index 85b65b8..3469b7e 100644
--- a/src/plugins/transfer_CLASS.cc
+++ b/src/plugins/transfer_CLASS.cc
@@ -25,7 +25,13 @@ private:
     std::vector<double> tab_lnk_, tab_dtot_, tab_dc_, tab_db_, tab_ttot_, tab_tc_, tab_tb_;
     gsl_interp_accel *gsl_ia_dtot_, *gsl_ia_dc_, *gsl_ia_db_, *gsl_ia_ttot_, *gsl_ia_tc_, *gsl_ia_tb_;
     gsl_spline *gsl_sp_dtot_, *gsl_sp_dc_, *gsl_sp_db_, *gsl_sp_ttot_, *gsl_sp_tc_, *gsl_sp_tb_;
-    double Omega_m_, Omega_b_, N_ur_, zstart_, ztarget_, kmax_, kmin_, h_;
+
+    // single fluid growing/decaying mode decomposition
+    gsl_interp_accel *gsl_ia_Cplus_, *gsl_ia_Cminus_;
+    gsl_spline *gsl_sp_Cplus_, *gsl_sp_Cminus_;
+    std::vector<double> tab_Cplus_, tab_Cminus_;
+
+    double Omega_m_, Omega_b_, N_ur_, zstart_, ztarget_, kmax_, kmin_, h_, astart_, atarget_;
 
     void ClassEngine_get_data( void ){
         std::vector<double> d_ncdm, t_ncdm, phi, psi;
@@ -37,25 +43,46 @@ private:
         pars.add("extra metric transfer functions", "yes");
         pars.add("z_pk",ztarget_);
         pars.add("P_k_max_h/Mpc", kmax_);
+        
         pars.add("h",h_);
         pars.add("Omega_b",Omega_b_);
         // pars.add("Omega_k",0.0);
         // pars.add("Omega_ur",0.0);
         pars.add("N_ur",N_ur_);
         pars.add("Omega_cdm",Omega_m_-Omega_b_);
-        pars.add("Omega_Lambda",1.0-Omega_m_);
-        // pars.add("Omega_fld",0.0);
-        // pars.add("Omega_scf",0.0);
+        pars.add("Omega_k",0.0);
+        // pars.add("Omega_Lambda",1.0-Omega_m_);
+        pars.add("Omega_fld",0.0);
+        pars.add("Omega_scf",0.0);
+
         pars.add("A_s",2.42e-9);
-        pars.add("n_s",.96); // tnis doesn't matter for TF
+        pars.add("n_s",.961); // this doesn't matter for TF
         pars.add("output","dTk,vTk");
         pars.add("YHe",0.248);
+        pars.add("lensing","no");
+        pars.add("alpha_s",0.0);
+        pars.add("P_k_ini type","analytic_Pk");
+        pars.add("gauge","synchronous");
+
+        pars.add("k_per_decade_for_pk",100);
+        pars.add("k_per_decade_for_bao",100);
 
-        pars.add("k_per_decade_for_pk",50);
-        pars.add("k_per_decade_for_bao",50);
         pars.add("compute damping scale","yes");
         pars.add("z_reio",-1.0); // make sure reionisation is not included
 
+        pars.add("tol_perturb_integration",1.e-8);
+        pars.add("tol_background_integration",1e-9);
+
+        // high precision options from cl_permille.pre:
+        // precision file to be passed as input in order to achieve at least percent precision on scalar Cls
+        pars.add("hyper_flat_approximation_nu", 7000. );
+        pars.add("transfer_neglect_delta_k_S_t0", 0.17 );
+        pars.add("transfer_neglect_delta_k_S_t1", 0.05 );
+        pars.add("transfer_neglect_delta_k_S_t2", 0.17 );
+        pars.add("transfer_neglect_delta_k_S_e", 0.13 );
+        pars.add("delta_l_max", 1000 );
+
+
         std::unique_ptr<ClassEngine> CE = std::make_unique<ClassEngine>(pars, false);
 
         CE->getTk(ztarget_, tab_lnk_, tab_dc_, tab_db_, d_ncdm, tab_dtot_,
@@ -74,7 +101,9 @@ public:
     Omega_b_ = pcf_->GetValue<double>("cosmology","Omega_b");
     N_ur_    = pcf_->GetValueSafe<double>("cosmology","N_ur", 3.046);
     ztarget_ = pcf_->GetValueSafe<double>("cosmology","ztarget",0.0);
+    atarget_ = 1.0/(1.0+ztarget_);
     zstart_  = pcf_->GetValue<double>("setup","zstart");
+    astart_  = 1.0/(1.0+zstart_);
     double lbox = pcf_->GetValue<double>("setup","BoxLength");
     int nres = pcf_->GetValue<double>("setup","GridRes");
     kmax_    = 2.0*M_PI/lbox * nres/2 * sqrt(3) * 2.0; // 120% of spatial diagonal
@@ -102,6 +131,33 @@ public:
     gsl_spline_init(gsl_sp_tc_,   &tab_lnk_[0], &tab_tc_[0],   tab_lnk_.size());
     gsl_spline_init(gsl_sp_tb_,   &tab_lnk_[0], &tab_tb_[0],   tab_lnk_.size());
 
+    //--------------------------------------------------------------------------
+    // single fluid growing/decaying mode decomposition
+    //--------------------------------------------------------------------------
+    gsl_ia_Cplus_  = gsl_interp_accel_alloc();
+    gsl_ia_Cminus_ = gsl_interp_accel_alloc();
+    
+    gsl_sp_Cplus_  = gsl_spline_alloc(gsl_interp_cspline, tab_lnk_.size());
+    gsl_sp_Cminus_ = gsl_spline_alloc(gsl_interp_cspline, tab_lnk_.size());
+    
+    tab_Cplus_.assign(tab_lnk_.size(),0);
+    tab_Cminus_.assign(tab_lnk_.size(),0);
+
+    std::ofstream ofs("grow_decay.txt");
+    
+    for( size_t i=0; i<tab_lnk_.size(); ++i ){
+      tab_Cplus_[i]  = (3.0/5.0 * tab_dtot_[i]/atarget_ - 2.0/5.0*tab_ttot_[i]/atarget_);
+      tab_Cminus_[i] = (2.0/5.0 * std::pow(atarget_, 1.5) *  ( tab_dtot_[i] + tab_ttot_[i] ));
+
+      ofs << std::exp(tab_lnk_[i]) << " " << tab_Cplus_[i] << " " << tab_Cminus_[i] << " " << tab_dtot_[i] << " " << tab_ttot_[i] << std::endl;
+    }
+    
+    gsl_spline_init(gsl_sp_Cplus_,   &tab_lnk_[0], &tab_Cplus_[0],   tab_lnk_.size());
+    gsl_spline_init(gsl_sp_Cminus_,  &tab_lnk_[0], &tab_Cminus_[0],  tab_lnk_.size());
+    //--------------------------------------------------------------------------
+    
+    
+
     kmin_ = std::exp(tab_lnk_[0]);
   
     tf_distinct_ = true;