diff --git a/src/classes/PMusr.cpp b/src/classes/PMusr.cpp
index 0756c25f..9ce62938 100644
--- a/src/classes/PMusr.cpp
+++ b/src/classes/PMusr.cpp
@@ -799,6 +799,80 @@ void PMsrGlobalBlock::SetT0Bin(Double_t dval, Int_t idx)
   fT0[idx] = dval;
 }
 
+//--------------------------------------------------------------------------
+// GetAddT0BinSize (public)
+//--------------------------------------------------------------------------
+/**
+ * <p> get add T0 size of the addrun at index addRunIdx
+ *
+ * <b>return:</b>
+ * - addt0 value, if idx is within proper boundaries
+ * - -1, otherwise
+ *
+ * \param addRunIdx index of the addrun
+ */
+Int_t PMsrGlobalBlock::GetAddT0BinSize(UInt_t addRunIdx)
+{
+  if (fAddT0.empty())
+    return -1;
+
+  if (addRunIdx >= fAddT0.size())
+    return -1;
+
+  return fAddT0[addRunIdx].size();
+}
+
+//--------------------------------------------------------------------------
+// GetAddT0Bin (public)
+//--------------------------------------------------------------------------
+/**
+ * <p> get add T0 of the addrun (index addRunIdx) at index histoIdx
+ *
+ * <b>return:</b>
+ * - addt0 value, if indices are within proper boundaries
+ * - -1, otherwise
+ *
+ * \param addRunIdx index of the addrun
+ * \param histoIdx index of the add backward histo number value
+ */
+Double_t PMsrGlobalBlock::GetAddT0Bin(UInt_t addRunIdx, UInt_t histoIdx)
+{
+  if (fAddT0.empty())
+    return -1.0;
+
+  if (addRunIdx >= fAddT0.size())
+    return -1.0;
+
+  if (fAddT0[addRunIdx].empty())
+    return -1.0;
+
+  if (histoIdx >= fAddT0[addRunIdx].size())
+    return -1.0;
+
+  return fAddT0[addRunIdx][histoIdx];
+}
+
+//--------------------------------------------------------------------------
+// SetAddT0Bin (public)
+//--------------------------------------------------------------------------
+/**
+ * <p> set add T0 bin of the addrun at index histoNoIdx
+ *
+ * \param ival T0 bin
+ * \param addRunIdx addrun index
+ * \param histoNoIdx index whithin the fAddT0 vector where to set the value.
+ */
+void PMsrGlobalBlock::SetAddT0Bin(Double_t dval, UInt_t addRunIdx, UInt_t histoNoIdx)
+{
+  if (addRunIdx >= fAddT0.size())
+    fAddT0.resize(addRunIdx+1);
+
+  if (histoNoIdx >= fAddT0[addRunIdx].size())
+    fAddT0[addRunIdx].resize(histoNoIdx+1);
+
+  fAddT0[addRunIdx][histoNoIdx] = dval;
+}
+
 //--------------------------------------------------------------------------
 // GetFitRange (public)
 //--------------------------------------------------------------------------
diff --git a/src/include/PMusr.h b/src/include/PMusr.h
index d58da6e4..3728aa29 100644
--- a/src/include/PMusr.h
+++ b/src/include/PMusr.h
@@ -537,6 +537,9 @@ class PMsrGlobalBlock {
     virtual Int_t GetDataRange(UInt_t idx);
     virtual UInt_t GetT0BinSize() { return fT0.size(); }
     virtual Double_t GetT0Bin(UInt_t idx=0);
+    virtual UInt_t GetAddT0BinEntries() { return fAddT0.size(); }
+    virtual Int_t GetAddT0BinSize(UInt_t addRunIdx);
+    virtual Double_t GetAddT0Bin(UInt_t addRunIdx, UInt_t histoIdx);
     virtual Bool_t IsFitRangeInBin() { return fFitRangeInBins; }
     virtual Double_t GetFitRange(UInt_t idx);
     virtual Int_t GetFitRangeOffset(UInt_t idx);
@@ -545,6 +548,7 @@ class PMsrGlobalBlock {
     virtual void SetFitType(Int_t ival) { fFitType = ival; }
     virtual void SetDataRange(Int_t ival, Int_t idx);
     virtual void SetT0Bin(Double_t dval, Int_t idx=-1);
+    virtual void SetAddT0Bin(Double_t dval, UInt_t addRunIdx, UInt_t histoNoIdx);
     virtual void SetFitRangeInBins(Bool_t bval) { fFitRangeInBins = bval; }
     virtual void SetFitRange(Double_t dval, UInt_t idx);
     virtual void SetFitRangeOffset(Int_t ival, UInt_t idx);
@@ -553,7 +557,8 @@ class PMsrGlobalBlock {
   private:
     Int_t fFitType;           ///< fit type: 0=single histo fit, 2=asymmetry fit, 4=mu^- single histo fit, 8=non muSR fit
     Int_t fDataRange[4];      ///< data bin range (fit type 0, 2, 4)
-    PDoubleVector fT0;        ///< t0 bins (fit type 0, 2, 4). if fit type 0 -> f0, f1, f2, ...; if fit type
+    PDoubleVector fT0;        ///< t0 bins (fit type 0, 2, 4).  if fit type 0 -> f0, f1, f2, ...; if fit type 2, 4 -> f0, b0, f1, b1, ...
+    vector<PDoubleVector> fAddT0; ///< addt0 bins (fit type 0, 2, 4).  if fit type 0 -> f0, f1, f2, ...; if fit type 2, 4 -> f0, b0, f1, b1, ...
     Bool_t fFitRangeInBins;   ///< flag telling if fit range is given in time or in bins
     Double_t fFitRange[2];    ///< fit range in (us)
     Int_t fFitRangeOffset[2]; ///< if fit range is given in bins it can have the form fit fgb+n0 lgb-n1. This variable holds the n0 and n1.