diff --git a/lib/XYSampleData.cpp b/lib/XYSampleData.cpp
index de4d1b6..6a4d62b 100644
--- a/lib/XYSampleData.cpp
+++ b/lib/XYSampleData.cpp
@@ -38,13 +38,19 @@ const DSample & SampleFitResult::getChi2(const PlaceHolder ph __unused) const
 
 double SampleFitResult::getChi2PerDof(const Index s) const
 {
-    return chi2_[s]/static_cast<double>(nDof_);
+    return chi2_[s]/getNDof();
 }
 
 DSample SampleFitResult::getChi2PerDof(const PlaceHolder ph __unused) const
 {
-    return chi2_/static_cast<double>(nDof_);
+    return chi2_/getNDof();
 }
+
+double SampleFitResult::getNDof(void) const
+{
+    return static_cast<double>(nDof_);
+}
+
 const DoubleFunction & SampleFitResult::getModel(const Index s, 
                                                  const Index j) const
 {
@@ -210,6 +216,7 @@ SampleFitResult XYSampleData::fit(Minimizer &minimizer, const DVec &init,
     FitResult       sampleResult;
     SampleFitResult result;
     bool            initChi2;
+    DVec            initBuf = init;
     
     result.resize(nSample);
     result.chi2_.resize(nSample);
@@ -232,7 +239,11 @@ SampleFitResult XYSampleData::fit(Minimizer &minimizer, const DVec &init,
         initChi2 = (s == central);
         
         // fit
-        sampleResult = data_.fit(minimizer, init, modelVector);
+        sampleResult = data_.fit(minimizer, initBuf, modelVector);
+        if (s == central)
+        {
+            initBuf = sampleResult;
+        }
         
         // store result
         result[s]       = sampleResult;
diff --git a/lib/XYSampleData.hpp b/lib/XYSampleData.hpp
index 88279cc..f500994 100644
--- a/lib/XYSampleData.hpp
+++ b/lib/XYSampleData.hpp
@@ -46,6 +46,7 @@ public:
     const DSample &              getChi2(const PlaceHolder ph) const;
     double                       getChi2PerDof(const Index s = central) const;
     DSample                      getChi2PerDof(const PlaceHolder ph) const;
+    double                       getNDof(void) const;
     const DoubleFunction &       getModel(const Index s = central,
                                           const Index j = 0) const;
     const DoubleFunctionSample & getModel(const PlaceHolder ph,
diff --git a/lib/XYStatData.cpp b/lib/XYStatData.cpp
index ccd16cf..2b2f6e3 100644
--- a/lib/XYStatData.cpp
+++ b/lib/XYStatData.cpp
@@ -32,14 +32,14 @@ double FitResult::getChi2(void) const
     return chi2_;
 }
 
-Index FitResult::getNDof(void) const
-{
-    return nDof_;
-}
-
 double FitResult::getChi2PerDof(void) const
 {
-    return chi2_/static_cast<double>(nDof_);
+    return chi2_/getNDof();
+}
+
+double FitResult::getNDof(void) const
+{
+    return static_cast<double>(nDof_);
 }
 
 const DoubleFunction & FitResult::getModel(const Index j) const
@@ -219,7 +219,6 @@ FitResult XYStatData::fit(Minimizer &minimizer, const DVec &init,
     {
         chi2_.requestInit();
     }
-    
     // initial parameters
     const Index nPoint = getNFitPoint();
     DVec        fullInit = init;
diff --git a/lib/XYStatData.hpp b/lib/XYStatData.hpp
index 5dff489..9c832bf 100644
--- a/lib/XYStatData.hpp
+++ b/lib/XYStatData.hpp
@@ -45,8 +45,8 @@ public:
     virtual ~FitResult(void) = default;
     // access
     double                 getChi2(void) const;
-    Index                  getNDof(void) const;
     double                 getChi2PerDof(void) const;
+    double                 getNDof(void) const;
     const DoubleFunction & getModel(const Index j = 0) const;
 private:
     double                      chi2_{0.0};