diff --git a/docs/sfcalc-help.txt b/docs/sfcalc-help.txt
index 5449006a..ce368dd7 100644
--- a/docs/sfcalc-help.txt
+++ b/docs/sfcalc-help.txt
@@ -17,6 +17,7 @@ Options:
   --dmin=NUM           Calculate structure factors up to given resolution.
   --for=TYPE           TYPE is xray (default), electron, neutron or mott-bethe.
   --normalize-it92     Normalize X-ray form factors (a tiny change).
+  --use-charge         Use X-ray form factors with charges when available.
   --ciffp              Read f' from _atom_type_scat_dispersion_real in CIF.
   --wavelength=NUM     Wavelength [A] for calculation of f' (use --wavelength=0
                        or -w0 to ignore anomalous scattering).
@@ -37,12 +38,14 @@ Options for anisotropic scaling (only w/ FFT):
                        Argument: FILE[:FCOL[:SIGFCOL]] (defaults: F and SIGF).
   --sigma-cutoff=NUM   Use only data with F/SIGF > NUM (default: 0).
 
-Options for bulk solvent correction (only w/ FFT):
+Options for bulk solvent correction and scaling (only w/ FFT):
+  --d-mask=NUM         Mask grid spacing (default: same as for model).
   --radii-set=SET      Set of per-element radii, one of: vdw, cctbx, refmac.
   --r-probe=NUM        Value added to VdW radius (default: 1.0A).
   --r-shrink=NUM       Value for shrinking the solvent area (default: 1.1A).
   --ksolv=NUM          Value (if optimizing: initial value) of k_solv.
   --bsolv=NUM          Value (if optimizing: initial value) of B_solv.
+  --kov=NUM            Value (if optimizing: initial value) of k_overall.
   --baniso=B11:...:B23 Anisotropic scale matrix (6 colon-separated numbers: B11,
                        B22, B33, B12, B13, B23).
 
diff --git a/include/gemmi/scaling.hpp b/include/gemmi/scaling.hpp
index 708ad8b1..066ed9a9 100644
--- a/include/gemmi/scaling.hpp
+++ b/include/gemmi/scaling.hpp
@@ -211,6 +211,12 @@ struct Scaling {
     return k_overall * std::exp(-0.25 * b_star.r_u_r(hkl));
   }
 
+  std::complex<Real> get_fcalc(const Point& p) const {
+    if (!use_solvent)
+      return p.fcmol;
+    return p.fcmol + (Real)get_solvent_scale(p.stol2) * p.fmask;
+  }
+
   // quick linear fit (ignoring sigma) to get initial parameters
   void fit_isotropic_b_approximately() {
     double sx = 0, sy = 0, sxx = 0, sxy = 0;
@@ -218,9 +224,8 @@ struct Scaling {
     for (const Point& p : points) {
       if (p.fobs < 1 || p.fobs < p.sigma)  // skip weak reflections
         continue;
+      double fcalc = std::abs(get_fcalc(p));
       double x = p.stol2;
-      double fcalc = std::abs(use_solvent ? p.fcmol + (Real)get_solvent_scale(x) * p.fmask
-                                          : p.fcmol);
       double y = std::log(static_cast<float>(p.fobs / fcalc));
       sx += x;
       sy += y;
@@ -237,6 +242,19 @@ struct Scaling {
     set_b_overall({b_iso, b_iso, b_iso, 0, 0, 0});
   }
 
+  double lsq_k_overall() const {
+    double sxx = 0, sxy = 0;
+    for (const Point& p : points) {
+      if (p.fobs < 1 || p.fobs < p.sigma)  // skip weak reflections
+        continue;
+      double x = std::abs(get_fcalc(p));
+      double y = p.fobs;
+      sxx += x * x;
+      sxy += x * y;
+    }
+    return sxx != 0. ? sxy / sxx : 1.;
+  }
+
   void fit_parameters() {
     LevMar levmar;
     levmar.fit(*this);
@@ -248,7 +266,7 @@ struct Scaling {
     std::vector<double> values;
     values.reserve(points.size());
     for (const Point& p : points) {
-      double fcalc = std::abs(p.fcmol + (Real)get_solvent_scale(p.stol2) * p.fmask);
+      double fcalc = std::abs(get_fcalc(p));
       values.push_back(fcalc * (Real) get_overall_scale_factor(p.hkl));
     }
     return values;
diff --git a/include/gemmi/solmask.hpp b/include/gemmi/solmask.hpp
index 14ac0ed6..fc5160c2 100644
--- a/include/gemmi/solmask.hpp
+++ b/include/gemmi/solmask.hpp
@@ -213,6 +213,7 @@ struct SolventMasker {
   double rshrink;
   double island_min_volume;
   double constant_r;
+  double requested_spacing = 0.;
 
   SolventMasker(AtomicRadiiSet choice, double constant_r_=0.) {
     set_radii(choice, constant_r_);
diff --git a/prog/sfcalc.cpp b/prog/sfcalc.cpp
index db73d7ed..96623dd1 100644
--- a/prog/sfcalc.cpp
+++ b/prog/sfcalc.cpp
@@ -31,9 +31,11 @@
 namespace {
 
 enum OptionIndex {
-  Hkl=4, Dmin, For, NormalizeIt92, Rate, Blur, RCut, Test, ToMtz, Compare,
+  Hkl=4, Dmin, For, NormalizeIt92, UseCharge, Rate, Blur, RCut,
+  Test, ToMtz, Compare,
   CifFp, Wavelength, Unknown, NoAniso, Margin, ScaleTo, SigmaCutoff, FLabel,
-  PhiLabel, Ksolv, Bsolv, Baniso, RadiiSet, Rprobe, Rshrink, WriteMap
+  PhiLabel, Ksolv, Bsolv, Kov, Baniso,
+  MaskSpacing, RadiiSet, Rprobe, Rshrink, WriteMap
 };
 
 struct SfCalcArg: public Arg {
@@ -84,6 +86,8 @@ const option::Descriptor Usage[] = {
     "  --for=TYPE  \tTYPE is xray (default), electron, neutron or mott-bethe." },
   { NormalizeIt92, 0, "", "normalize-it92", Arg::None,
     "  --normalize-it92  \tNormalize X-ray form factors (a tiny change)." },
+  { UseCharge, 0, "", "use-charge", Arg::None,
+    "  --use-charge  \tUse X-ray form factors with charges when available." },
   { CifFp, 0, "", "ciffp", Arg::None,
     "  --ciffp  \tRead f' from _atom_type_scat_dispersion_real in CIF." },
   { Wavelength, 0, "w", "wavelength", Arg::Float,
@@ -119,7 +123,10 @@ const option::Descriptor Usage[] = {
     "  --sigma-cutoff=NUM  \tUse only data with F/SIGF > NUM (default: 0)." },
   // TODO: solvent option: mask, babinet, none
 
-  { NoOp, 0, "", "", Arg::None, "\nOptions for bulk solvent correction (only w/ FFT):" },
+  { NoOp, 0, "", "", Arg::None,
+    "\nOptions for bulk solvent correction and scaling (only w/ FFT):" },
+  { MaskSpacing, 0, "", "d-mask", Arg::Float,
+    "  --d-mask=NUM  \tMask grid spacing (default: same as for model)." },
   { RadiiSet, 0, "", "radii-set", SfCalcArg::Radii,
     "  --radii-set=SET  \tSet of per-element radii, one of: vdw, cctbx, refmac." },
   { Rprobe, 0, "", "r-probe", Arg::Float,
@@ -130,6 +137,8 @@ const option::Descriptor Usage[] = {
     "  --ksolv=NUM  \tValue (if optimizing: initial value) of k_solv." },
   { Bsolv, 0, "", "bsolv", Arg::Float,
     "  --bsolv=NUM  \tValue (if optimizing: initial value) of B_solv." },
+  { Kov, 0, "", "kov", Arg::Float,
+    "  --kov=NUM  \tValue (if optimizing: initial value) of k_overall." },
   { Baniso, 0, "", "baniso", SfCalcArg::Float6,
     "  --baniso=B11:...:B23 \tAnisotropic scale matrix (6 colon-separated numbers: "
       "B11, B22, B33, B12, B13, B23)." },
@@ -283,19 +292,37 @@ void process_with_fft(const gemmi::Structure& st,
 
   gemmi::AsuData<std::complex<Real>> mask_data;
   if (scaling.use_solvent) {
-    // uses scaling.grid as a temporary array
-    masker.put_mask_on_grid(dencalc.grid, st.models[0]);
-    mask_data = transform_map_to_f_phi(dencalc.grid, /*half_l=*/true)
+    // by default, use DensityCalculator::grid as a temporary array
+    auto mask_grid = &dencalc.grid;
+    std::unique_ptr<gemmi::Grid<Real>> custom_grid;
+    if (masker.requested_spacing != 0) {
+      custom_grid.reset(new gemmi::Grid<Real>());
+      custom_grid->unit_cell = dencalc.grid.unit_cell;
+      custom_grid->spacegroup = dencalc.grid.spacegroup;
+      custom_grid->set_size_from_spacing(masker.requested_spacing,
+                                         gemmi::GridSizeRounding::Up);
+      mask_grid = custom_grid.get();
+      fprintf(stderr, "Solvent mask grid: %d x %d x %d\n",
+              mask_grid->nu, mask_grid->nv, mask_grid->nw);
+    }
+    masker.put_mask_on_grid(*mask_grid, st.models[0]);
+    mask_data = transform_map_to_f_phi(*mask_grid, /*half_l=*/true)
                 .prepare_asu_data(dencalc.d_min, 0);
   }
 
   if (scale_to.size() != 0) {
     scaling.prepare_points(asu_data, scale_to, &mask_data);
     printf("Calculating scale factors using %zu points...\n", scaling.points.size());
-    scaling.fit_isotropic_b_approximately();
-    //fprintf(stderr, "k_ov=%g B_ov=%g\n", scaling.k_overall, scaling.get_b_overall().u11);
-    scaling.fit_parameters();
     gemmi::SMat33<double> b_aniso = scaling.get_b_overall();
+    if (b_aniso.all_zero()) {
+      scaling.fit_isotropic_b_approximately();
+      //fprintf(stderr, "initial k_ov=%g B_ov=%g\n",
+      //        scaling.k_overall, scaling.get_b_overall().u11);
+    } else if (scaling.k_overall == 1.) {
+      scaling.k_overall = scaling.lsq_k_overall();
+      //fprintf(stderr, "initial k_ov=%g\n", scaling.k_overall);
+    }
+    scaling.fit_parameters();
     if (scaling.use_solvent)
       fprintf(stderr, "Bulk solvent parameters: k_sol=%g B_sol=%g\n",
               scaling.k_sol, scaling.b_sol);
@@ -666,6 +693,8 @@ void process_with_table(bool use_st, gemmi::Structure& st, const gemmi::SmallStr
         masker.rprobe = std::atof(p.options[Rprobe].arg);
       if (p.options[Rshrink])
         masker.rshrink = std::atof(p.options[Rshrink].arg);
+      if (p.options[MaskSpacing])
+        masker.requested_spacing = std::atof(p.options[MaskSpacing].arg);
 
       gemmi::Scaling<Real> scaling(cell, st.find_spacegroup());
       if (p.options[Ksolv] || p.options[Bsolv] || scale_to.size() != 0) {
@@ -675,6 +704,8 @@ void process_with_table(bool use_st, gemmi::Structure& st, const gemmi::SmallStr
         if (p.options[Bsolv])
           scaling.b_sol = std::atof(p.options[Bsolv].arg);
       }
+      if (p.options[Kov])
+        scaling.k_overall = std::atof(p.options[Kov].arg);
       if (p.options[Baniso]) {
         char* endptr = nullptr;
         gemmi::SMat33<double> b_aniso;
@@ -805,10 +836,9 @@ void process(const std::string& input, const OptParser& p) {
   if (p.options[CifFp] && table != 'x')
     gemmi::fail("Electron scattering has no dispersive part (--ciffp)");
   if (table == 'x' || table == 'm') {
+    gemmi::IT92<float>::ignore_charge = (table == 'm' || !p.options[UseCharge]);
     if (p.options[NormalizeIt92])
       gemmi::IT92<float>::normalize();
-    if (table == 'm')
-      gemmi::IT92<float>::ignore_charge = true;
     process_with_table<gemmi::IT92<float>>(use_st, st, small, wavelength,
                                            table == 'm', p);
   } else if (table == 'e') {