diff --git a/SS_biofxn.tpl b/SS_biofxn.tpl
index 00acbfc8..ecf9aafe 100644
--- a/SS_biofxn.tpl
+++ b/SS_biofxn.tpl
@@ -1532,19 +1532,14 @@ FUNCTION void get_wtlen()
           wt_len(s, gp).shift(1);
         }
 
-        //  SS_Label_Info_19.2.3  #calculate first diff of wt_len for use in generalized sizp comp bin calculations
         if (gg == gender)
         {
           wt_len2_sq(s, GPat) = elem_prod(wt_len2(s, GPat), wt_len2(s, GPat));
-          wt_len_fd(s, GPat) = first_difference(wt_len_low(s, GPat));
-          if (gender == 2)
-            wt_len_fd(s, GPat, nlength) = wt_len_fd(s, GPat, nlength - 1);
   #ifdef DO_ONCE
           if (do_once == 1)
             echoinput << "wtlen2 " << endl
                       << wt_len2 << endl
-                      << "wtlen2^2 " << wt_len2_sq << endl
-                      << "wtlen2:firstdiff " << wt_len_fd << endl;
+                      << "wtlen2^2 " << wt_len2_sq << endl;
   #endif
         }
       }
diff --git a/SS_expval.tpl b/SS_expval.tpl
index df6fb5eb..21c213e0 100644
--- a/SS_expval.tpl
+++ b/SS_expval.tpl
@@ -666,7 +666,6 @@ FUNCTION void Get_expected_values(const int y, const int t);
               {
                 if (SzFreq_Nmeth > 0) //  have some sizefreq data
                 {
-
                   if (have_data(ALK_time, f, data_type, 0) > 0)
                   {
                     for (j = 1; j <= have_data(ALK_time, f, data_type, 0); j++) // loop all obs of this type
@@ -674,252 +673,126 @@ FUNCTION void Get_expected_values(const int y, const int t);
                       iobs = have_data(ALK_time, f, data_type, j); //  observation index
                       SzFreqMethod = SzFreq_obs_hdr(iobs, 6);
                       SzFreqMethod_seas = nseas * (SzFreqMethod - 1) + s; // index that combines sizefreqmethod and season and used in SzFreqTrans
-                      if (SzFreq_obs_hdr(iobs, 9) > 0) // first occurrence of this method at this time is with fleet = f
+                      for (gg = 1; gg <= gender; gg++)
                       {
-                        if (do_once == 1 || (MG_active(3) > 0 && (timevary_MG(y, 3) > 0))) // calc  matrix because wtlen parameters have changed
+                        if (gg == 1)
                         {
-                          for (gg = 1; gg <= gender; gg++)
-                          {
-                            if (gg == 1)
-                            {
-                              z1 = 1;
-                              z2 = nlength;
-                              ibin = 0;
-                              ibinsave = 0;
-                            } // female
-                            else
-                            {
-                              z1 = nlength1;
-                              z2 = nlength2;
-                              ibin = 0;
-                              ibinsave = SzFreq_Nbins(SzFreqMethod);
-                            } // male
-                            topbin = 0.;
-                            botbin = 0.;
-
-                            //  NOTE:  wt_len_low is  calculated separately for each growth pattern (GPat)
-                            //  but the code below still just uses GPat=1 for calculation of the sizefreq transition matrix
-
-                            switch (SzFreq_units(SzFreqMethod)) // biomass vs. numbers are accumulated in the bins
-                            {
-                              case (1): // units are biomass, so accumulate body weight into the bins;  Assume that bin demarcations are also in biomass
-                              {
-                                if (SzFreq_Omit_Small(SzFreqMethod) == 1)
-                                {
-                                  while (wt_len_low(s, 1, z1 + 1) < SzFreq_bins(SzFreqMethod, 1) && z1 < z2)
-                                  {
-                                    z1++;
-                                  }
-                                } // ignore tiny fish
-                                if (z1 + 1 >= z2)
-                                {
-                                  warnstream << "max population size " << wt_len_low(s, 1, z1) << " is less than first data bin " << SzFreq_bins(SzFreqMethod, 1) << " for SzFreqMethod " << SzFreqMethod;
-                                  write_message (FATAL, 0); // EXIT!
-                                }
-
-                                if (wt_len_low(s, 1, nlength2) < SzFreq_bins(SzFreqMethod, SzFreq_Nbins(SzFreqMethod)))
-                                {
-                                  warnstream << "max population size " << wt_len_low(s, 1, nlength2) << " is less than max data bin " << SzFreq_bins(SzFreqMethod, SzFreq_Nbins(SzFreqMethod)) << " for SzFreqMethod " << SzFreqMethod;
-                                  write_message (FATAL, 0); // EXIT!
-                                }
-
-                                for (z = z1; z <= z2; z++)
-                                {
-                                  if (ibin == SzFreq_Nbins(SzFreqMethod))
-                                  {
-                                    SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = wt_len2(s, 1, z);
-                                  }
-                                  else
-                                  {
-                                    if (wt_len_low(s, 1, z) >= topbin)
-                                    {
-                                      ibin++;
-                                      ibinsave++;
-                                    }
-                                    if (ibin > 1)
-                                    {
-                                      botbin = SzFreq_bins2(SzFreqMethod, ibin);
-                                    }
-                                    if (ibin == SzFreq_Nbins(SzFreqMethod))
-                                    {
-                                      SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = wt_len2(s, 1, z);
-                                      topbin = 99999.;
-                                    }
-                                    else
-                                    {
-                                      topbin = SzFreq_bins2(SzFreqMethod, ibin + 1);
-                                      if (wt_len_low(s, 1, z) >= botbin && wt_len_low(s, 1, z + 1) <= topbin)
-                                      {
-                                        SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = wt_len2(s, 1, z);
-                                      }
-                                      else
-                                      {
-                                        temp = (wt_len_low(s, 1, z + 1) - topbin) / wt_len_fd(s, 1, z); // frac in pop bin above (data bin +1)
-                                        temp1 = wt_len_low(s, 1, z) + (1. - temp * 0.5) * wt_len_fd(s, 1, z); // approx body wt for these fish
-                                        temp2 = wt_len_low(s, 1, z) + (1. - temp) * 0.5 * wt_len_fd(s, 1, z); // approx body wt for  fish below
-                                        SzFreqTrans(SzFreqMethod_seas, z, ibinsave + 1) = temp * temp1;
-                                        SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = (1. - temp) * temp2;
-                                      }
-                                    }
-                                  }
-                                }
-                                if (SzFreq_scale(SzFreqMethod) == 2 && gg == gender) // convert to pounds
-                                {
-                                  SzFreqTrans(SzFreqMethod_seas) /= 0.4536;
-                                }
-                                break;
-                              } //  end of units in biomass
-                              // NOTE: even though  the transition matrix is currently in units of biomass distribution, there is no need to
-                              // normalize to sum to 1.0 here because the normalization will occur after it gets used to create SzFreq_exp
-
-                              case (2): // units are numbers
-                              {
-                                if (SzFreq_scale(SzFreqMethod) <= 2) //  bin demarcations are in weight units (1=kg, 2=lbs), so uses wt_len to compare to bins
-                                {
-                                  if (SzFreq_Omit_Small(SzFreqMethod) == 1)
-                                  {
-                                    while (wt_len_low(s, 1, z1 + 1) < SzFreq_bins(SzFreqMethod, 1) && z1 < z2)
-                                    {
-                                      z1++;
-                                    }
-                                  } // ignore tiny fish
-                                  if (z1 + 1 >= z2)
-                                  {
-                                    warnstream << "max population size " << wt_len_low(s, 1, z1) << " is less than first data bin " << SzFreq_bins(SzFreqMethod, 1) << " for SzFreqMethod " << SzFreqMethod;
-                                    write_message (FATAL, 0); // EXIT!
-                                  }
-                                  if (wt_len_low(s, 1, nlength2) < SzFreq_bins(SzFreqMethod, SzFreq_Nbins(SzFreqMethod)))
-                                  {
-                                    warnstream << "max population size " << wt_len_low(s, 1, nlength2) << " is less than max data bin " << SzFreq_bins(SzFreqMethod, SzFreq_Nbins(SzFreqMethod)) << " for SzFreqMethod " << SzFreqMethod;
-                                    write_message (FATAL, 0); // EXIT!
-                                  }
-
-                                  for (z = z1; z <= z2; z++)
-                                  {
-                                    if (ibin == SzFreq_Nbins(SzFreqMethod))
-                                    {
-                                      SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1.;
-                                    } //checkup<<" got to last ibin, so put rest of popbins here"<<endl;
-                                    else
-                                    {
-                                      if (wt_len_low(s, 1, z) >= topbin)
-                                      {
-                                        ibin++;
-                                        ibinsave++;
-                                      } //checkup<<" incr ibin "<<z<<" "<<ibin<<" "<<len_bins(z)<<" "<<len_bins_dat(ibin);
-                                      if (ibin > 1)
-                                      {
-                                        botbin = SzFreq_bins2(SzFreqMethod, ibin);
-                                      }
-                                      if (ibin == SzFreq_Nbins(SzFreqMethod)) // checkup<<" got to last ibin, so put rest of popbins here"<<endl;
-                                      {
-                                        SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1.;
-                                        topbin = 99999.;
-                                      }
-                                      else
-                                      {
-                                        topbin = SzFreq_bins2(SzFreqMethod, ibin + 1);
-                                        if (wt_len_low(s, 1, z) >= botbin && wt_len_low(s, 1, z + 1) <= topbin) //checkup<<" pop inside dat, put here"<<endl;
-                                        {
-                                          SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1.;
-                                        }
-                                        else // checkup<<" overlap"<<endl;
-                                        {
-                                          SzFreqTrans(SzFreqMethod_seas, z, ibinsave + 1) = (wt_len_low(s, 1, z + 1) - topbin) / wt_len_fd(s, 1, z);
-                                          SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1. - SzFreqTrans(SzFreqMethod_seas, z, ibinsave + 1);
-                                        }
-                                      }
-                                    }
-                                  }
-                                }
-
-                                else //  bin demarcations are in length unit (3=cm, 4=inch) so uses population len_bins to compare to data bins
-                                {
-                                  if (SzFreq_Omit_Small(SzFreqMethod) == 1)
-                                  {
-                                    while (len_bins2(z1 + 1) < SzFreq_bins(SzFreqMethod, 1))
-                                    {
-                                      z1++;
-                                    }
-                                    //  echoinput<<"accumulate starting at bin: "<<z1<<endl;
-                                  } // ignore tiny fish
-
-                                  if (len_bins2(nlength2) < SzFreq_bins(SzFreqMethod, SzFreq_Nbins(SzFreqMethod)))
-                                  {
-                                    warnstream << "max population len bin " << len_bins2(nlength2) << " is less than max data bin " << SzFreq_bins(SzFreqMethod, SzFreq_Nbins(SzFreqMethod)) << " for SzFreqMethod " << SzFreqMethod;
-                                    write_message (FATAL, 0); // EXIT!
-                                  }
+                          z1 = 1;
+                          z2 = nlength;
+                        } // female
+                        else
+                        {
+                          z1 = nlength1;
+                          z2 = nlength2;
+                        } // male
+
+                        //  NOTE:  wt_len_low is  calculated separately for each growth pattern (GPat)
+                        //  but the code below still just uses GPat=1 for calculation of the sizefreq transition matrix
+                        dvector src_edges(1, nlength + 1); // +1 to create a dummy bin holding upper edge of the actual last bin
+                        src_edges(1, nlength) = len_bins(1, nlength); 
+                        src_edges(nlength + 1) = src_edges(nlength) + (src_edges(nlength) - src_edges(nlength - 1));
+                        dvar_vector dest_edges(1,SzFreq_Nbins(SzFreqMethod) + 1);  // +1 to create a dummy bin holding upper edge of the actual last bin
+                        dvar_vector dest_edges_wt(1,SzFreq_Nbins(SzFreqMethod) + 1);
+                        dest_edges.initialize();
+                        for (ibin = 1; ibin <= SzFreq_Nbins(SzFreqMethod); ibin++) {
+                          dest_edges(ibin) = SzFreq_bins(SzFreqMethod, ibin);
+                          dest_edges_wt(ibin) = dest_edges(ibin);  // save in raw units
+                        }
+                        dest_edges(SzFreq_Nbins(SzFreqMethod) + 1) = 99999.;
+                        dest_edges_wt(ibin) = dest_edges_wt(ibin - 1) + (dest_edges_wt(ibin - 1) - dest_edges_wt(ibin - 2));
+                        if(SzFreq_Omit_Small(SzFreqMethod) < 0.0)
+                        {
+                          dest_edges(1) = 0.; //  so src_bins smaller than first actual dest_bin are included in first bin
+                        }
 
-                                  for (z = z1; z <= z2; z++)
-                                  {
-                                    if (ibin == SzFreq_Nbins(SzFreqMethod))
-                                    {
-                                      SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1.;
-                                    } //checkup<<" got to last ibin, so put rest of popbins here"<<endl;
-                                    else
-                                    {
-                                      if (len_bins2(z) >= topbin)
-                                      {
-                                        ibin++;
-                                        ibinsave++;
-                                      } //checkup<<" incr ibin "<<z<<" "<<ibin<<" "<<len_bins(z)<<" "<<len_bins_dat(ibin);
-                                      if (ibin > 1)
-                                      {
-                                        botbin = SzFreq_bins2(SzFreqMethod, ibin);
-                                      }
-                                      if (ibin == SzFreq_Nbins(SzFreqMethod)) // checkup<<" got to last ibin, so put rest of popbins here"<<endl;
-                                      {
-                                        SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1.;
-                                        topbin = 99999.;
-                                      }
-                                      else
-                                      {
-                                        topbin = SzFreq_bins2(SzFreqMethod, ibin + 1);
-                                        if (len_bins2(z) >= botbin && len_bins2(z + 1) <= topbin) //checkup<<" pop inside dat, put here"<<endl;
-                                        {
-                                          SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1.;
-                                        }
-                                        else // checkup<<" overlap"<<endl;
-                                        {
-                                          SzFreqTrans(SzFreqMethod_seas, z, ibinsave + 1) = (len_bins2(z + 1) - topbin) / (len_bins2(z + 1) - len_bins2(z));
-                                          SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = 1. - SzFreqTrans(SzFreqMethod_seas, z, ibinsave + 1);
-                                        }
-                                      }
-                                    }
-                                  }
-                                }
-                                break;
-                              } //  end of units in numbers
-                            }
-                            if (docheckup == 1 && gg == gender)
-                              echoinput << " sizefreq trans_matrix: method/season " << SzFreqMethod << " / " << s << endl
-                                        << trans(SzFreqTrans(SzFreqMethod_seas)) << endl;
-                          } // end gender loop
-                        } //  end needing to calc the matrix because it may have changed
-                      } // done calculating the SzFreqTransition matrix for this method
+                        dvar_vector dest_comp(1,SzFreq_Nbins(SzFreqMethod));  //  destination composition.  one-sex at a time
+                      // convert dest_edges to cm
+                      // as in the legacy method, this conversion is sex and season specific, but only uses Gpat = 1
+                      switch (SzFreq_scale(SzFreqMethod)) // biomass vs. numbers are accumulated in the bins
+                      {
+                        case (1): // scale is kg
+                        {
+                          // fall thru to calcs in the lb case
+                        }
+                        case (2): // scale is lb, or fall thru from kg
+                        {
+                  // bin boundary in lb have already been converted to kg
+                  // wt_len(s, gp) is potentially by season and by Gpat within sex.  Here, only Gpat==1 will be used.  It will be sex-specific
+                  // W=a*L^b; so L = exp((ln(W)-ln(a))/B)
+                          dvariable wtlen_a;
+                          dvariable wtlen_b;
+                          GPat = 1;  // this means that any (unusual) use of multiple Gpatterns will still use biology of GPat 1 for szfreq purposes
+                          // female parms are at 1, 2; males at 7,8
+                          int parm_loc = 1 + (gg - 1) * 6;
+                          wtlen_a = wtlen_p(GPat, parm_loc);
+                          wtlen_b = wtlen_p(GPat, parm_loc + 1);
+                          if (MGparm_seas_effects(1) > 0 || MGparm_seas_effects(2) > 0) //  get seasonal effect on wtlen parameters
+                          {
+                            wtlen_a *= wtlen_seas(s, GPat, parm_loc);
+                            wtlen_b *= wtlen_seas(s, GPat, parm_loc + 1);
+                          }
+                          dest_edges = exp((log(dest_edges)-log(wtlen_a))/wtlen_b);
+                          break;
+                        }
+                        case (3):  //  scale is in cm
+                        {
+                          break;
+                        }
+                        case 4:  // scale is in inches.  Already converted to cm in readdata.  Relic feature for some ancient recreational fishery data
+                        {
+                          break;
+                        }
+                      }  // end calc of new dest_edges
+                      if (do_once == 1) echoinput << "Szfreq_method: " << SzFreqMethod << "  sex: " << gg << " dest_edges_converted_to_cm "<<dest_edges<<endl;
 
+                      dvar_vector pass_comp(z1, z2);  // this gets males or females range according to z1, z2
+                      pass_comp.initialize();
                       switch (SzFreq_obs_hdr(iobs, 5)) // discard/retained partition
                       {
                         case (0):
                         {
-                          SzFreq_exp(iobs) = trans(SzFreqTrans(SzFreqMethod_seas)) * exp_l_temp;
+                          pass_comp = exp_l_temp(z1, z2);
+                  //                          SzFreq_exp(iobs) = trans(SzFreqTrans(SzFreqMethod_seas)) * exp_l_temp;
                           break;
                         }
                         case (1):
                         {
-                          SzFreq_exp(iobs) = trans(SzFreqTrans(SzFreqMethod_seas)) * (exp_l_temp - exp_l_temp_ret);
+                          pass_comp = exp_l_temp(z1, z2) - exp_l_temp_ret(z1, z2);
+                  //                         SzFreq_exp(iobs) = trans(SzFreqTrans(SzFreqMethod_seas)) * (exp_l_temp - exp_l_temp_ret);
                           break;
                         }
                         case (2):
                         {
-                          SzFreq_exp(iobs) = trans(SzFreqTrans(SzFreqMethod_seas)) * exp_l_temp_ret;
+                          pass_comp = exp_l_temp_ret(z1, z2);
+                          // SzFreq_exp(iobs) = trans(SzFreqTrans(SzFreqMethod_seas)) * exp_l_temp_ret;
                           break;
                         }
                       }
-  #ifdef DO_ONCE
-                      if (do_once == 1)
-                        echoinput << y << " " << f << " szfreq_exp_initial  " << SzFreq_exp(iobs) << endl;
-  #endif
+                      int use_GP;
+                      use_GP = 1;
+                      if (gg == 2) {use_GP += N_GP;}  // because GPat is nested in sex; only GPat 1 bio gets used for szfreq data
+                      pass_comp.shift(1);  // change index to 1
+                      if (SzFreq_units(SzFreqMethod) == 1) // biomass is accumulated in the bins
+                      {
+                        dvar_vector pass_src_wt(z1, z2+1);
+                        pass_src_wt(z1,z2) = wt_len_low(s, 1)(z1,z2);  //  just one sex's range is passed
+                        pass_src_wt.shift(1);  // change index to 1
+                        dest_comp = rebin_bio(src_edges, pass_comp, dest_edges, pass_src_wt, dest_edges_wt);
+                      }
+                      else
+                      {
+                        dest_comp = rebin(src_edges, pass_comp, dest_edges);
+                      }
+                      if( gg == 1)
+                      {
+                        SzFreq_exp(iobs)(1, SzFreq_Nbins(SzFreqMethod)) = dest_comp;
+                      }
+                      else
+                      {
+                        dest_comp.shift(SzFreq_Nbins(SzFreqMethod) + 1);
+                        SzFreq_exp(iobs)(SzFreq_Nbins(SzFreqMethod) + 1, 2 * SzFreq_Nbins(SzFreqMethod)) = dest_comp;
+                      }
+                      } // end gender loop
 
                       if (gender == 2)
                       {
@@ -984,10 +857,9 @@ FUNCTION void Get_expected_values(const int y, const int t);
                           SzFreq_exp(iobs)(1, k) /= sum(SzFreq_exp(iobs)(1, k));
                         }
                       }
-  #ifdef DO_ONCE
+
                       if (do_once == 1)
-                        echoinput << y << " " << f << " szfreq_exp_final  " << SzFreq_exp(iobs) << endl;
-  #endif
+                        echoinput << y << " fleet: " << f << "  method: " << SzFreqMethod << " szfreq_exp_after_add_mincomp  " << SzFreq_exp(iobs) << endl;
                     } // end loop of obs for fleet = f
                   } //  end having some obs for this method in this fleet
                 } //  end use of generalized size freq data
diff --git a/SS_miscfxn.tpl b/SS_miscfxn.tpl
index 76964cb3..554b7caa 100644
--- a/SS_miscfxn.tpl
+++ b/SS_miscfxn.tpl
@@ -120,3 +120,129 @@ FUNCTION dvariable Comp_logL_Dirichlet(const double& Nsamp, const dvariable& dir
     logL = sum(gammln(Nsamp * obs_comp + dirichlet_Parm * exp_comp)) - sum(gammln(dirichlet_Parm * exp_comp));
     return (logL);
   }
+
+  
+FUNCTION dvar_vector rebin(const dvector& src_edges, const dvar_vector& src_counts, const dvar_vector& dest_edges)
+  {
+    /*
+    This implementation takes two vectors representing the boundaries (edges) of the source
+    and destination bins, and one vector for the source counts.
+
+    Rebins frequency data from one set of boundaries to another.
+    @param src_edges Boundaries of the original bins (size N+1).
+    @param src_counts Frequency/counts in original bins (size N).
+    @param dest_edges Boundaries of the new bins (size M+1).
+    @return Vector of rebinned frequency data (size M).
+    src_counts need not be counts; works for real number of fish, or for biomass of fish.
+    However, if src_counts are in biomass units, this rebin method does not account for fact that fish in lower portion of a src bin
+       will weigh less than fish in upper portion.
+    the original code searched all source bins for each destination bins.
+    Here the ordered characteristic of the bins allows for the search for bin (i+1) to continue from search for bin(i).
+    */
+
+    dvar_vector dest_counts(1, dest_edges.size() - 1);  // size to leave off the topbin bounary
+    dest_counts.initialize();
+    int j_start = 1;
+    for (int i = 1; i <= dest_counts.size(); i++) {
+        dvariable d_low = dest_edges[i];
+        dvariable d_high = dest_edges[i + 1];
+
+        // Advance j_start if the source bin is entirely below the current destination bin.
+        // Because d_low increases with 'i', j_start only ever moves forward.
+        while (j_start <= src_counts.size() && src_edges[j_start + 1] <= d_low) {
+            j_start++;
+        }
+
+        // Iterate through source bins starting from j_start, but stop as soon 
+        // as the source bin is completely above the current destination bin.
+        for (int j = j_start; j <= src_counts.size() && src_edges[j] < d_high; j++) {
+            dvariable s_low = src_edges[j];
+            dvariable s_high = src_edges[j + 1];
+            // Calculate the overlap bounds
+            dvariable overlap_low = d_low;
+            if (s_low > d_low) overlap_low = s_low;
+            
+            dvariable overlap_high = d_high;
+            if (s_high < d_high) overlap_high = s_high;
+//            echoinput<<"rebin: dest: "<<i<<" "<<dest_edges[i]<<" src: "<<j<<" "<<src_edges[j]<<" overlap_lo "<<overlap_low <<" overlap_hi "<<overlap_high <<  endl;
+
+            // If there is valid overlap, distribute the counts
+            if (overlap_low < overlap_high) {
+                dvariable overlap_width = overlap_high - overlap_low;
+                dvariable src_bin_width = s_high - s_low;
+                dest_counts[i] += src_counts[j] * (overlap_width / src_bin_width);
+//                echoinput<<"add src to dest: "<<dest_edges[i]<<" "<<src_edges[j]<<" result: "<<(overlap_width / src_bin_width)<<endl;
+            }
+        }
+      }
+    return (dest_counts);
+  }
+
+FUNCTION dvar_vector rebin_bio(const dvector& src_edges, const dvar_vector& src_counts, const dvar_vector& dest_edges, const dvar_vector& src_edges_wt, const dvar_vector& dest_edges_wt )
+  {
+    /*
+    This modification of rebin is used when biomass is accumulated into the bins
+    for example, with catch weight composition
+    it takes into account the fact that fish in the lower portion of a length bin have less body weight than fish in the opper portion of the length bin
+    NOTE:  need to undo the conversion of numbers to biomass in SS_expval.  It needs to occur here.
+    legacy szfreq method used this approach:
+      temp = (wt_len_low(s, 1, z + 1) - topbin) / wt_len_fd(s, 1, z); // frac in pop bin above (data bin +1)
+      temp1 = wt_len_low(s, 1, z) + (1. - temp * 0.5) * wt_len_fd(s, 1, z); // approx body wt for these fish
+      temp2 = wt_len_low(s, 1, z) + (1. - temp) * 0.5 * wt_len_fd(s, 1, z); // approx body wt for  fish below
+      SzFreqTrans(SzFreqMethod_seas, z, ibinsave + 1) = temp * temp1;
+      SzFreqTrans(SzFreqMethod_seas, z, ibinsave) = (1. - temp) * temp2;
+    new approach has access to the body wt at boundaries of size range of fish getting rebinned, so will use that to get more exact body weights
+    */
+    dvar_vector dest_counts(1, dest_edges.size() - 1);  // sized to leave off the topbin boundary
+    dest_counts.initialize();
+    int j_start = 1;
+    for (int i = 1; i <= dest_counts.size(); i++) {  // loop the destination bins
+        dvariable d_low = dest_edges[i];
+        dvariable d_high = dest_edges[i + 1];
+        // Advance j_start if the source bin is entirely below the current destination bin.
+        // Because d_low increases with 'i', j_start only ever moves forward.
+        while (j_start <= src_counts.size() && src_edges[j_start + 1] <= d_low) {
+            j_start++;
+        }
+        // Iterate through source bins starting from j_start, but stop as soon 
+        // as the source bin is completely above the current destination bin.
+        for (int j = j_start; j <= src_counts.size() && src_edges[j] < d_high; j++) {
+          dvariable s_low = src_edges[j];
+          dvariable s_high = src_edges[j + 1];
+          // Calculate the overlap bounds
+          dvariable overlap_low = d_low;
+          if (s_low > d_low) overlap_low = s_low;
+          
+          dvariable overlap_high = d_high;
+          if (s_high < d_high) overlap_high = s_high;
+
+          // If there is valid overlap, distribute the counts
+          if (overlap_low < overlap_high) {
+            dvariable overlap_width = overlap_high - overlap_low;
+            dvariable src_bin_width = s_high - s_low;
+
+            // get mean weight of fish in range of src being assigned to dest
+            // d_low and d_high are the original weight bin boundaries (assumes the weight comp data always uses weight bin boundaries)
+            // s_low and s_high have weights stored in wt_len_low(s,GPat)
+            //  src_edges_wt, dest_edges_wt
+            dvariable mean_szwt;  // body weight of fish to be allocated from src to dest
+            if (s_low >= d_low)
+            {
+              if (s_high <= d_high)  // src entirely in dest range range
+                {mean_szwt = (src_edges_wt[j] + src_edges_wt[j+1]) * 0.5;}
+              else //  s_high > d_high; calc mean size from s_low and d_high
+                {mean_szwt = (src_edges_wt[j] + dest_edges_wt[i+1]) * 0.5;}
+            }
+            else if (s_high <= d_high )  // overlap with s_low < d_low; calc the mean size from d_low and s_high 
+              {mean_szwt = (dest_edges_wt[i] + src_edges_wt[j+1]) * 0.5;}
+            else  // s_high > d_high, so dest bin is internal to src_bin
+              {mean_szwt = (dest_edges_wt[i] + dest_edges_wt[i+1]) * 0.5;}
+
+              dest_counts[i] += src_counts[j] * mean_szwt * (overlap_width / src_bin_width);  // add overlap fraction of biomass to dest
+            //  echoinput<<" src: "<<j<<" lo_hi "<<s_low << " "<<s_high<<" dest: "<<i<<" lo_hi "<<d_low<<" "<<d_high<<" overlap: "<<overlap_low <<" "<<overlap_high
+            //  <<" fraction: "<<(overlap_width / src_bin_width)<<" mean: "<<mean_szwt<<endl;
+          }  // end having overlap to be allocated
+        }  // end j loop of source bins
+      }
+    return (dest_counts);
+  }
\ No newline at end of file
diff --git a/SS_param.tpl b/SS_param.tpl
index feab63af..e602f2f0 100644
--- a/SS_param.tpl
+++ b/SS_param.tpl
@@ -97,7 +97,6 @@ PARAMETER_SECTION
   3darray wt_len2(1,nseas,1,N_GP,1,nlength2)    //  stores wt at midbin; stacked genders
   3darray wt_len2_sq(1,nseas,1,N_GP,1,nlength2)    //  stores wt at midbin^2; stacked genders
   3darray wt_len_low(1,nseas,1,N_GP,1,nlength2)  //  wt at lower edge of size bin
-  3darray wt_len_fd(1,nseas,1,N_GP,1,nlength2-1)  //  first diff of wt_len_low
 
   matrix mat_len(1,N_GP,1,nlength)
   matrix fec_len(1,N_GP,1,nlength)   // fecundity at length
diff --git a/SS_prelim.tpl b/SS_prelim.tpl
index 633a5f42..f520d9eb 100644
--- a/SS_prelim.tpl
+++ b/SS_prelim.tpl
@@ -1353,7 +1353,6 @@
   get_mat_fec();
   wt_len = value(wt_len);
   wt_len2 = value(wt_len2);
-  wt_len_fd = value(wt_len_fd);
   mat_len = value(mat_len);
   mat_fec_len = value(mat_fec_len);
   mat_age = value(mat_age);
diff --git a/SS_readdata_330.tpl b/SS_readdata_330.tpl
index b8fac5ff..c06c1838 100644
--- a/SS_readdata_330.tpl
+++ b/SS_readdata_330.tpl
@@ -3136,7 +3136,7 @@
   init_ivector SzFreq_nobs(1,SzFreq_Nmeth);
 !!if (SzFreq_Nmeth > 0) echoinput << SzFreq_nobs << " Sizefreq N obs per method" << endl;
   ivector SzFreq_Nbins_seas_g(1,SzFreq_Nmeth*nseas);   //  array dimensioner used only for the SzFreqTrans array
-  ivector SzFreq_Nbins3(1,SzFreq_Nmeth);      // doubles the Nbins if gender==2
+  ivector SzFreq_Nbins3(1,SzFreq_Nmeth);      // values will be doubled if gender==2
   int SzFreqMethod_seas;
   ivector Comp_Err_Sz(1,SzFreq_Nmeth);
   ivector Comp_Err_Sz2(1,SzFreq_Nmeth);
@@ -3196,7 +3196,6 @@
     }
   }
   // clang-format off
-  echoinput<<"here"<<endl;
  END_CALCS
 
  !!echoinput<<"bins "<<SzFreq_Nbins<<endl;
@@ -3266,9 +3265,14 @@
           SzFreq_means(k, z) = SzFreq_means(k, z - 1) + (SzFreq_bins2(k, z) - SzFreq_bins2(k, z - 1));
         }
         if (gender == 2)
+        {
           SzFreq_means(k, z + SzFreq_Nbins(k)) = SzFreq_means(k, z);
+        }
       }
+//      SzFreq_bins2(k, SzFreq_Nbins(k)) = 99999.;
+//      if (gender == 2) SzFreq_bins2(k,SzFreq_Nbins(k) + SzFreq_Nbins(k) + 1) = 99999.;
       echoinput << "Processed_SizeFreqMethod_bins for method: " << k << endl
+                << "bins2: " << SzFreq_bins2(k) << endl
                 << "low: " << SzFreq_bins(k) << endl
                 << "mean: " << SzFreq_means(k) << endl;
     }
diff --git a/SS_write_report.tpl b/SS_write_report.tpl
index 0c08d496..5aadffb6 100644
--- a/SS_write_report.tpl
+++ b/SS_write_report.tpl
@@ -3624,7 +3624,7 @@ FUNCTION void write_bigoutput()
       for (f1 = 1; f1 <= N_pred; f1++)
       {
         f = predator(f1);
-        SS2out << fleetname(f) << "_M2 comsume_Bio consume_Num";
+        SS2out << fleetname(f) << "_M2 consume_Bio consume_Num";
       }
       SS2out << endl;
       for (y = styr - 2; y <= YrMax; y++)