diff --git a/FDTD/engine_multithread.cpp b/FDTD/engine_multithread.cpp
index 44b4121..2e78bc2 100644
--- a/FDTD/engine_multithread.cpp
+++ b/FDTD/engine_multithread.cpp
@@ -96,6 +96,10 @@ void Engine_Multithread::Init()
 	if (m_numThreads == 0)
 		m_numThreads = boost::thread::hardware_concurrency();
 
+	vector<unsigned int> m_Start_Lines;
+	vector<unsigned int> m_Stop_Lines;
+	m_Op_MT->CalcStartStopLines( m_numThreads, m_Start_Lines, m_Stop_Lines );
+
 	cout << "Multithreaded engine using " << m_numThreads << " threads. Utilization: (";
 	m_barrier_VoltUpdate = new boost::barrier(m_numThreads); // numThread workers
 	m_barrier_VoltExcite = new boost::barrier(m_numThreads+1); // numThread workers + 1 excitation thread
@@ -110,15 +114,14 @@ void Engine_Multithread::Init()
 	m_startBarrier = new boost::barrier(m_numThreads+1); // numThread workers + 1 controller
 	m_stopBarrier = new boost::barrier(m_numThreads+1); // numThread workers + 1 controller
 
-	unsigned int linesPerThread = round((float)numLines[0] / (float)m_numThreads);
 	for (unsigned int n=0; n<m_numThreads; n++)
 	{
-		unsigned int start = n * linesPerThread;
-		unsigned int stop = (n+1) * linesPerThread - 1;
+		unsigned int start = m_Start_Lines.at(n);
+		unsigned int stop = m_Stop_Lines.at(n);
 		unsigned int stop_h = stop;
-		if (n == m_numThreads-1) {
+		if (n == m_numThreads-1)
+		{
 			// last thread
-			stop = numLines[0]-1;
 			stop_h = stop-1;
 			cout << stop-start+1 << ")" << endl;
 		}
diff --git a/FDTD/operator_multithread.cpp b/FDTD/operator_multithread.cpp
index ee10356..56f12eb 100644
--- a/FDTD/operator_multithread.cpp
+++ b/FDTD/operator_multithread.cpp
@@ -74,14 +74,32 @@ void Operator_Multithread::Reset()
 	delete m_CalcPEC_Stop;m_CalcPEC_Stop=NULL;
 }
 
+void Operator_Multithread::CalcStartStopLines(unsigned int &numThreads, vector<unsigned int> &start, vector<unsigned int> &stop) const
+{
+	unsigned int linesPerThread = round((float)numLines[0] / (float)numThreads);
+	if ((numThreads-1) * linesPerThread >= numLines[0])
+		--numThreads;
+
+	start.resize(numThreads);
+	stop.resize(numThreads);
+
+	for (unsigned int n=0; n<numThreads; n++)
+	{
+		start.at(n) = n * linesPerThread;
+		stop.at(n) = (n+1) * linesPerThread - 1;
+		if (n == numThreads-1) // last thread
+			stop.at(n) = numLines[0]-1;
+	}
+}
+
 int Operator_Multithread::CalcECOperator()
 {
 	if (m_numThreads == 0)
 		m_numThreads = boost::thread::hardware_concurrency();
 
-	unsigned int linesPerThread = round((float)numLines[0] / (float)m_numThreads);
-	if ((m_numThreads-1) * linesPerThread >= numLines[0])
-		--m_numThreads;
+	vector<unsigned int> m_Start_Lines;
+	vector<unsigned int> m_Stop_Lines;
+	CalcStartStopLines( m_numThreads, m_Start_Lines, m_Stop_Lines );
 
 	cout << "Multithreaded operator using " << m_numThreads << " threads." << std::endl;
 
@@ -94,12 +112,7 @@ int Operator_Multithread::CalcECOperator()
 
 	for (unsigned int n=0; n<m_numThreads; n++)
 	{
-		unsigned int start = n * linesPerThread;
-		unsigned int stop = (n+1) * linesPerThread - 1;
-		if (n == m_numThreads-1) // last thread
-			stop = numLines[0]-1;
-
-		boost::thread *t = new boost::thread( Operator_Thread(this,start,stop,n) );
+		boost::thread *t = new boost::thread( Operator_Thread(this,m_Start_Lines.at(n),m_Stop_Lines.at(n),n) );
 		m_thread_group.add_thread( t );
 	}
 
diff --git a/FDTD/operator_multithread.h b/FDTD/operator_multithread.h
index d6333d2..70dcd1d 100644
--- a/FDTD/operator_multithread.h
+++ b/FDTD/operator_multithread.h
@@ -56,6 +56,14 @@ protected:
 
 	boost::thread_group m_thread_group;
 	unsigned int m_numThreads; // number of worker threads
+
+	//! Calculate the start/stop lines for the multithreading operator and engine.
+	/*!
+		It depends on the number of threads and number of lines to simulate.
+		This method is also used by the multithreading engine!
+		This method may also reduce the usable number of thread in case of too few lines or otherwise bad utilization.
+	*/
+	virtual void CalcStartStopLines(unsigned int &numThreads, vector<unsigned int> &start, vector<unsigned int> &stop) const;
 };
 
 class Operator_Thread