diff --git a/lib/tdm_ripper.cpp b/lib/tdm_ripper.cpp
index c6b6a0f..d4da6fd 100644
--- a/lib/tdm_ripper.cpp
+++ b/lib/tdm_ripper.cpp
@@ -279,6 +279,40 @@ void tdm_ripper::list_channels(std::ostream& gout, int width, int maxshow)
   }
 }
 
+void tdm_ripper::list_groups(std::ostream& gout, int width, int maxshow)
+{
+  gout<<std::setw(width)<<"group";
+  gout<<std::setw(width)<<"group id";
+  gout<<std::setw(width)<<"group name";
+  gout<<std::setw(width)<<"num channels";
+  gout<<"\n";
+  gout<<std::setfill('-')<<std::setw(4*width+1)<<"\n";
+  gout<<std::setfill(' ');
+
+  for ( int i = 0; i < num_groups_ && i < maxshow; i++ )
+  {
+    gout<<std::setw(width)<<i+1;
+    gout<<std::setw(width)<<group_id_[i];
+    gout<<std::setw(width)<<group_name_[i];
+    gout<<std::setw(width)<<num_channels_group_[i];
+    gout<<"\n";
+  }
+  gout<<"\n\n";
+
+  if ( num_channels_ > maxshow )
+  {
+    for ( int i = num_groups_-maxshow; i < num_channels_; i++ )
+    {
+      gout<<std::setw(width)<<i+1;
+      gout<<std::setw(width)<<group_id_[i];
+      gout<<std::setw(width)<<group_name_[i];
+      gout<<std::setw(width)<<num_channels_group_[i];
+      gout<<"\n";
+    }
+    gout<<"\n\n";
+  }
+}
+
 void tdm_ripper::show_structure()
 {
   int width = 25;
@@ -444,11 +478,13 @@ std::vector<double> tdm_ripper::get_channel(int channelid)
   std::vector<double> chann = convert_channel(channel_ext_[channelid-1]);
 
   // check if converted value is within expected range
-  for ( int i = 0; i < (int)chann.size(); i++ )
-  {
-    assert( chann[i] >= minmax_[channelid-1].first  - 1.0e-10
-         && chann[i] <= minmax_[channelid-1].second + 1.0e-10 );
-  }
+  // for ( int i = 0; i < (int)chann.size(); i++ )
+  // {
+  //   if ( chann[i] < minmax_[channelid-1].first
+  //     || chann[i] > minmax_[channelid-1].second ) std::cout<<std::setw(20)<<chann[i]<<std::setw(20)<<minmax_[channelid-1].first<<std::setw(20)<<minmax_[channelid-1].second<<"\n";
+  //   assert( chann[i] >= minmax_[channelid-1].first  - 1.0e-6
+  //        && chann[i] <= minmax_[channelid-1].second + 1.0e-6 );
+  // }
 
   return chann;
 }
diff --git a/lib/tdm_ripper.hpp b/lib/tdm_ripper.hpp
index 149029a..d376d1f 100644
--- a/lib/tdm_ripper.hpp
+++ b/lib/tdm_ripper.hpp
@@ -61,6 +61,7 @@ public:
   void parse_structure();
 
   void list_channels(std::ostream& gout = std::cout, int width = 15, int maxshow = 50);
+  void list_groups(std::ostream& gout = std::cout, int width = 15, int maxshow = 50);
 
   void show_structure();
 
@@ -148,9 +149,11 @@ public:
   {
     return num_groups_;
   }
+
+  // get number of channels in specific group
   const int& no_channels(int groupid)
   {
-    assert( groupid > 0 && groupid <= num_channels_ );
+    assert( groupid > 0 && groupid <= num_groups_ );
 
     return num_channels_group_[groupid-1];
   }
@@ -162,6 +165,28 @@ public:
     return channel_name_[channelid-1];
   }
 
+  // obtain overall channel id from combined group and group-specific channel id
+  int obtain_channel_id(int groupid, int channelid)
+  {
+    assert( groupid > 0 && groupid <= num_groups_ );
+    assert( channelid > 0 && channelid <= num_channels_group_[groupid-1] );
+
+    // find cummulative number of channels
+    int numsum = 0;
+    for ( int i = 0; i < groupid-1; i++ )
+    {
+      numsum += num_channels_group_[i];
+    }
+    assert( (numsum + channelid) > 0 && (numsum + channelid) <= num_channels_ );
+
+    return numsum+channelid;
+  }
+
+  const std::string& channel_name(int groupid, int channelid)
+  {
+    return channel_name_[obtain_channel_id(groupid,channelid)-1];
+  }
+
   const std::string& group_name(int groupid)
   {
     assert( groupid > 0 && groupid <= num_channels_ );
@@ -169,6 +194,11 @@ public:
     return group_name_[groupid-1];
   }
 
+  const std::string& channel_unit(int groupid, int channelid)
+  {
+    return units_[obtain_channel_id(groupid,channelid)-1];
+  }
+
   void list_datatypes();
 
   // convert array of chars to single integer or floating point double
@@ -183,7 +213,13 @@ public:
   // std::vector<double> convert_channel(int byteoffset, int length, int typesize);
   std::vector<double> convert_channel(int channelid);
 
+  // obtain channel from overall channel id...
   std::vector<double> get_channel(int channelid);
+  // ...or from group id and group-specific channel id
+  std::vector<double> channel(int groupid, int channelid)
+  {
+    return get_channel(obtain_channel_id(groupid,channelid));
+  }
 
   void print_channel(int channelid, const char* filename, int width = 15);
 
diff --git a/main.cpp b/main.cpp
index 75ffb8b..615eb1c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -22,25 +22,34 @@ int main(int argc, char* argv[])
   ripper.list_channels(fout);
   fout.close();
 
-  std::cout<<"number of channels "<<ripper.num_channels()<<"\n\n";
+  ripper.list_groups();
+  std::ofstream gout("data/list_of_groups.dat");
+  ripper.list_groups(gout);
+  gout.close();
+
+  std::cout<<"number of channels "<<ripper.num_channels()<<"\n";
   std::cout<<"number of groups "<<ripper.num_groups()<<"\n\n";
 
-  for ( int i = 0; i < ripper.num_groups(); i++ )
-  {
-    std::cout<<std::setw(10)<<i+1<<std::setw(10)<<ripper.no_channels(i+1)<<"\n";
-  }
+  // for ( int i = 0; i < ripper.num_groups(); i++ )
+  // {
+  //   std::cout<<std::setw(10)<<i+1<<std::setw(10)<<ripper.no_channels(i+1)<<"\n";
+  //   for ( int j = 0; j < ripper.no_channels(i+1); j++ )
+  //   {
+  //     std::cout<<std::setw(10)<<i+1<<std::setw(10)<<j+1<<std::setw(30)<<ripper.channel_name(i+1,j+1)<<"\n";
+  //   }
+  // }
 
   // std::vector<double> channA = ripper.get_channel(1);
   // for ( auto el: channA ) std::cout<<el<<"\n";
   // std::cout<<"\n\n";
 
-  // for ( int i = 0; i < 30; i++ )
-  // // for ( int i = 0; i < ripper.num_channels(); i++ )
-  // // for ( int i = 11880; i < ripper.num_channels(); i++ )
-  // {
-  //   ripper.print_channel(i+1,("data/channel_"+std::to_string(i+1)+"_"
-  //                                       +ripper.channel_name(i+1)+".dat").c_str());
-  // }
+  for ( int i = 3; i < 10; i++ )
+  // for ( int i = 0; i < ripper.num_channels(); i++ )
+  // for ( int i = 11880; i < ripper.num_channels(); i++ )
+  {
+    ripper.print_channel(i+1,("data/channel_"+std::to_string(i+1)+"_"
+                                        +ripper.channel_name(i+1)+".dat").c_str());
+  }
 
   return 0;
 }
diff --git a/pytdm_ripper.pyx b/pytdm_ripper.pyx
index 1922611..e7ebb18 100644
--- a/pytdm_ripper.pyx
+++ b/pytdm_ripper.pyx
@@ -21,18 +21,32 @@ cdef class pytdmripper:
 
     def no_channels(self, int groupid):
         assert (groupid >= 0 and groupid < self.cripp.num_groups()), "index of group must be in [0,n-1]"
-        groupidinc = groupid+1
-        return self.cripp.no_channels(groupidinc)
+        return self.cripp.no_channels(groupid+1)
 
     def num_groups(self):
         return self.cripp.num_groups()
 
+    def no_channel_groups(self):
+        return self.cripp.num_groups()
+
+    def channel_name(self,int groupid,int channelid):
+        return self.cripp.channel_name(groupid+1,channelid+1).decode('utf-8')
+
+    def channel_unit(self,int groupid,int channelid):
+        return (self.cripp.channel_unit(groupid+1,channelid+1))
+
     def get_channel(self, int channelid):
         return np.asarray(self.cripp.get_channel(channelid))
 
+    def channel(self,int groupid,int channelid):
+        return self.cripp.channel(groupid+1,channelid+1)
+
     def print_channel(self, int channelid, const char* filename):
         self.cripp.print_channel(channelid,filename)
 
+    def close(self):
+        dummy = ""
+
     # integrate into CONTI_HBS workflow by adding methods: (29.04.2019)
     #   tdm_loader.OpenFile(tmp_path + name_prefix + '/Messung.tdm', encoding='utf-8')
     #   .no_channel_groups()
diff --git a/tdm_ripper.pxd b/tdm_ripper.pxd
index c0b229a..3e57732 100644
--- a/tdm_ripper.pxd
+++ b/tdm_ripper.pxd
@@ -15,5 +15,11 @@ cdef extern from "tdm_ripper.hpp":
         int num_channels()
         int no_channels(int)
         int num_groups()
+        int no_channel_groups()
+        string channel_name(int,int)
+        string channel_unit(int,int)
         vector[double] get_channel(int)
+        vector[double] channel(int,int)
         void print_channel(int,const char*)
+        # dummy method for compatibility
+        void close()