diff --git a/src/index_base.cc b/src/index_base.cc
index 1b47e70..352cc52 100644
--- a/src/index_base.cc
+++ b/src/index_base.cc
@@ -34,6 +34,18 @@ namespace MultiArrayTools
 	return mRangePtr->size();
     }
 
+    bool IndexBase::locked() const
+    {
+	return mLocked;
+    }
+    
+    IndexBase& IndexBase::lock(std::shared_ptr<const IndexBase>& idx)
+    {
+	mLocked = (idx.get() == this);
+	return *this;
+    }
+
+    
     IndexBase::operator size_t() const
     {
 	return pos();
diff --git a/src/index_base.h b/src/index_base.h
index a0278f8..27a40ac 100644
--- a/src/index_base.h
+++ b/src/index_base.h
@@ -54,6 +54,9 @@ namespace MultiArrayTools
 	virtual bool last() const = 0;
 	virtual bool first() const = 0;
 
+	virtual bool locked() const;
+	virtual IndexBase& lock(std::shared_ptr<const IndexBase>& idx);
+	
 	virtual std::shared_ptr<const IndexBase> getPtr(size_t n) const = 0;
 	
 	virtual operator size_t() const;
@@ -64,6 +67,7 @@ namespace MultiArrayTools
 	std::shared_ptr<RangeBase> mRangePtr;
 	size_t mPos;
 	size_t mId;
+	bool mLocked = false;
     };
 
     template <typename MetaType>
diff --git a/src/multi_array_operation.cc b/src/multi_array_operation.cc
index ea825c1..0589bb7 100644
--- a/src/multi_array_operation.cc
+++ b/src/multi_array_operation.cc
@@ -106,6 +106,8 @@ namespace MultiArrayTools
 	    std::dynamic_pointer_cast<MultiRange<Ranges...> >( mrf.create() );
 	mIndex = std::make_shared<IndexType>( mr->begin() );
 	(*mIndex) = *index;
+	// -> find optimal block index !!!
+	// -> lock this index !!!
 	for(*mIndex = 0; mIndex->pos() != mIndex->max(); ++(*mIndex)){
 	    get() = mSecond.get();
 	}
@@ -114,13 +116,15 @@ namespace MultiArrayTools
     template <typename T, class... Ranges>
     BlockBase<T>& OperationMaster<T,Ranges...>::get()
     {
-	return mArrayRef.data()[ mIndex->pos() ];
+	block();
+	return *mBlockPtr;
     }
     
     template <typename T, class... Ranges>
     const BlockBase<T>& OperationMaster<T,Ranges...>::get() const
     {
-	return mArrayRef.data()[ mIndex->pos() ];
+	block();
+	return *mBlockPtr;
     }
 
     template <typename T, class... Ranges>
diff --git a/src/multi_array_operation.h b/src/multi_array_operation.h
index 9e8fc69..80d1830 100644
--- a/src/multi_array_operation.h
+++ b/src/multi_array_operation.h
@@ -34,6 +34,7 @@ namespace MultiArrayTools
 
     BlockType getBlockType(std::shared_ptr<const IndexBase> i,
 			   std::shared_ptr<const IndexBase> j, bool first);
+
     
     template <typename T>
     class OperationBase
@@ -120,6 +121,7 @@ namespace MultiArrayTools
 	OperationBase<T> const& mSecond;
 	MutableMultiArrayBase<T,Ranges...>& mArrayRef;
 	std::shared_ptr<IndexType> mIndex;
+
     };
 
     
diff --git a/src/multi_range.cc b/src/multi_range.cc
index 3fe6107..71ee330 100644
--- a/src/multi_range.cc
+++ b/src/multi_range.cc
@@ -47,6 +47,7 @@ namespace MultiArrayTools
     {
 	PackNum<sizeof...(Indices)-1>::construct(mIPack, *range);
 	IB::mPos = PackNum<sizeof...(Indices)-1>::makePos(mIPack);
+	PackNum<sizeof...(Indices)>::initBlockSizes(mBlockSizes, mIPack); // has one more element!
     }
 
     template <class... Indices>
@@ -58,16 +59,15 @@ namespace MultiArrayTools
     template <class... Indices>
     MultiIndex<Indices...>& MultiIndex<Indices...>::operator++()
     {
-	PackNum<sizeof...(Indices)-1>::pp( mIPack );
-	++IB::mPos;
+	// return step size -> add to IB::mPos
+	IB::mPos += PackNum<sizeof...(Indices)-1>::pp( mIPack, mBlockSizes );
 	return *this;
     }
 
     template <class... Indices>
     MultiIndex<Indices...>& MultiIndex<Indices...>::operator--()
     {
-	PackNum<sizeof...(Indices)-1>::mm( mIPack );
-	--IB::mPos;
+	IB::mPos -= PackNum<sizeof...(Indices)-1>::mm( mIPack, mBlockSizes );
 	return *this;
     }
     
@@ -175,6 +175,14 @@ namespace MultiArrayTools
 	return std::dynamic_pointer_cast<RangeType>( IB::mRangePtr );
     }
 
+    template <class... Indices>
+    MultiIndex<Indices...>& MultiIndex<Indices...>::lock(std::shared_ptr<const IndexBase>& idx)
+    {
+	IB::mLocked = (idx.get() == this);
+	PackNum<sizeof...(Indices)-1>::lock(mIPack, idx);
+	return *this;
+    }
+    
     template <class... Indices>
     MultiIndex<Indices...>& MultiIndex<Indices...>::operator()(std::shared_ptr<Indices>&... indices)
     {
diff --git a/src/multi_range.h b/src/multi_range.h
index 4aca29b..61c507e 100644
--- a/src/multi_range.h
+++ b/src/multi_range.h
@@ -27,7 +27,8 @@ namespace MultiArrayTools
 	
     protected:
 	IndexPack mIPack;
-
+	std::array<size_t,sizeof...(Indices)+1> mBlockSizes;
+	
     public:
 	MultiIndex() = delete;
 	// NO DEFAULT HERE !!!
@@ -70,6 +71,8 @@ namespace MultiArrayTools
 
 	std::shared_ptr<RangeType> range() const;
 
+	virtual MultiIndex& lock(std::shared_ptr<const IndexBase>& idx) override;
+	
 	// raplace instances (in contrast to its analogon in ContainerIndex
 	// MultiIndices CANNOT be influences be its subindices, so there is
 	// NO foreign/external controll)
diff --git a/src/pack_num.h b/src/pack_num.h
index f3d292f..6348cf7 100644
--- a/src/pack_num.h
+++ b/src/pack_num.h
@@ -49,31 +49,66 @@ namespace MultiArrayHelper
 		return PackNum<N-1>::getIndexPtr(in, n);
 	    }
 	}
+
+	template <class... Indices>
+	static void lock(std::tuple<std::shared_ptr<Indices>...>& ip,
+			 std::shared_ptr<const IndexBase>& toLock)
+	{
+	    std::get<N>(ip)->lock(toLock);
+	    PackNum<N-1>::lock(ip, toLock);
+	}
 	
 	template <class... Indices>
-	static inline void pp(std::tuple<std::shared_ptr<Indices>...>& ip)
+	static void initBlockSizes(std::array<size_t,sizeof...(Indices)+1>& bs,
+				   std::tuple<std::shared_ptr<Indices>...>& ip)
+	{
+	    if(N == sizeof...(Indices)){
+		std::get<N>(bs) = 1;
+	    }
+	    else {
+		std::get<N>(bs) = PackNum<sizeof...(Indices)-N-1>::blockSize(ip);
+		PackNum<N-1>::initBlockSizes(bs, ip);
+	    }
+	}
+	
+	template <class... Indices>
+	static inline size_t pp(std::tuple<std::shared_ptr<Indices>...>& ip,
+				std::array<size_t,sizeof...(Indices)>& bs)
 	{
 	    auto& si = *std::get<N>(ip);
-	    if(si.last()){
+	    if(si.last() or si.locked()){
 		si = 0;
 		PackNum<N-1>::pp(ip);
 	    }
 	    else {
 		++si;
 	    }
+	    if(si.locked()){
+		return std::get<N-1>(bs) - std::get<N>(bs) + 1;
+	    }
+	    else {
+		return 1;
+	    }
 	}
 	
 	template <class... Indices>
-	static inline void mm(std::tuple<std::shared_ptr<Indices>...>& ip)
+	static inline size_t mm(std::tuple<std::shared_ptr<Indices>...>& ip,
+				std::array<size_t,sizeof...(Indices)>& bs)
 	{
 	    auto& si = *std::get<N>(ip);
-	    if(si.first()){
+	    if(si.first() or si.locked()){
 		si = si.max();
 		PackNum<N-1>::mm(ip);
 	    }
 	    else {
 		--si;
 	    }
+	    if(si.locked()){
+		return std::get<N-1>(bs) - std::get<N>(bs) + 1;
+	    }
+	    else {
+		return 1;
+	    }
 	}
 	
 	template <class RangeTuple>
@@ -188,19 +223,50 @@ namespace MultiArrayHelper
 	{
 	    return in.template getPtr<0>();
 	}
-	
+
 	template <class... Indices>
-	static inline void pp(std::tuple<std::shared_ptr<Indices>...>& ip)
+	static void lock(std::tuple<std::shared_ptr<Indices>...>& ip,
+			 std::shared_ptr<const IndexBase>& toLock)
 	{
-	    auto& si = *std::get<0>(ip);
-	    ++si;
+	    std::get<0>(ip)->lock(toLock);
 	}
 	
 	template <class... Indices>
-	static inline void mm(std::tuple<std::shared_ptr<Indices>...>& ip)
+	static void initBlockSizes(std::array<size_t,sizeof...(Indices)+1>& bs,
+				   std::tuple<std::shared_ptr<Indices>...>& ip)
+	{
+	    std::get<0>(bs) = PackNum<sizeof...(Indices)-1>::blockSize(ip);
+	}
+	
+	template <class... Indices>
+	static inline size_t pp(std::tuple<std::shared_ptr<Indices>...>& ip,
+			      std::array<size_t,sizeof...(Indices)+1>& bs)
 	{
 	    auto& si = *std::get<0>(ip);
-	    --si;
+	    if(si.locked()){
+		si = si.max()+1;
+		return std::get<0>(bs) - std::get<1>(bs) + 1;
+	    }
+	    else {		
+		++si;
+		return 1;
+	    }
+	}
+	
+	template <class... Indices>
+	static inline size_t mm(std::tuple<std::shared_ptr<Indices>...>& ip,
+			      std::array<size_t,sizeof...(Indices)>& bs)
+	{
+	    auto& si = *std::get<0>(ip);
+	    if(si.locked()){
+		si = 0;
+		--si;
+		return std::get<0>(bs) - std::get<1>(bs) + 1;
+	    }
+	    else {		
+		--si;
+		return 1;
+	    }
 	}
 	
 	template <class RangeTuple>