diff --git a/src/main/java/de/neemann/digital/core/Model.java b/src/main/java/de/neemann/digital/core/Model.java
index 0803d7156..59b032334 100644
--- a/src/main/java/de/neemann/digital/core/Model.java
+++ b/src/main/java/de/neemann/digital/core/Model.java
@@ -8,11 +8,12 @@ import java.util.Collections;
  */
 public class Model {
 
-    private ArrayList<Node> nodes;
+    private final ArrayList<Node> nodes;
     private ArrayList<Node> nodesToUpdateAct;
     private ArrayList<Node> nodesToUpdateNext;
     private int version;
     private int maxCounter = 1000;
+    private Listener listener;
 
     public Model() {
         this.nodes = new ArrayList<>();
@@ -66,6 +67,8 @@ public class Model {
             if (counter++ > maxCounter) {
                 throw new NodeException("seemsToOscillate");
             }
+            if (listener != null)
+                listener.needsUpdate();
         }
     }
 
@@ -77,4 +80,8 @@ public class Model {
         nodesToUpdateNext.addAll(nodes);
         doStep(noise);
     }
+
+    public void setListener(Listener listener) {
+        this.listener = listener;
+    }
 }
diff --git a/src/main/java/de/neemann/digital/core/ObservableValue.java b/src/main/java/de/neemann/digital/core/ObservableValue.java
index 73633136f..3030058d4 100644
--- a/src/main/java/de/neemann/digital/core/ObservableValue.java
+++ b/src/main/java/de/neemann/digital/core/ObservableValue.java
@@ -45,6 +45,7 @@ public class ObservableValue extends Value {
     }
 
     public void setValue(long value) {
+        value = getValueBits(value);
         if (this.value != value) {
             this.value = value;
             if (!highZ)
@@ -52,12 +53,8 @@ public class ObservableValue extends Value {
         }
     }
 
-    public long getValueBits() {
-        return getValueBits(getValue());
-    }
-
     public long getValueBits(long value) {
-        return value & (1 << bits) - 1;
+        return value & ((1 << bits) - 1);
     }
 
     public void checkBits(ObservableValue value) throws BitsException {
diff --git a/src/main/java/de/neemann/digital/core/arithmetic/Add.java b/src/main/java/de/neemann/digital/core/arithmetic/Add.java
index 2746a4ddd..c539a491c 100644
--- a/src/main/java/de/neemann/digital/core/arithmetic/Add.java
+++ b/src/main/java/de/neemann/digital/core/arithmetic/Add.java
@@ -36,7 +36,7 @@ public class Add extends Node implements Part {
 
     @Override
     public void readInputs() throws NodeException {
-        value = a.getValueBits() + b.getValueBits() + c_in.getValueBits();
+        value = a.getValue() + b.getValue() + c_in.getValue();
     }
 
     @Override
diff --git a/src/main/java/de/neemann/digital/core/arithmetic/Mul.java b/src/main/java/de/neemann/digital/core/arithmetic/Mul.java
index 68999514e..fa519e7bb 100644
--- a/src/main/java/de/neemann/digital/core/arithmetic/Mul.java
+++ b/src/main/java/de/neemann/digital/core/arithmetic/Mul.java
@@ -28,7 +28,7 @@ public class Mul extends Node implements Part {
 
     @Override
     public void readInputs() throws NodeException {
-        value = a.getValueBits() * b.getValueBits();
+        value = a.getValue() * b.getValue();
     }
 
     @Override
diff --git a/src/main/java/de/neemann/digital/core/arithmetic/Sub.java b/src/main/java/de/neemann/digital/core/arithmetic/Sub.java
index 20504309e..4e96a3ac3 100644
--- a/src/main/java/de/neemann/digital/core/arithmetic/Sub.java
+++ b/src/main/java/de/neemann/digital/core/arithmetic/Sub.java
@@ -26,6 +26,6 @@ public class Sub extends Add {
 
     @Override
     public void readInputs() throws NodeException {
-        value = a.getValueBits() - b.getValueBits() - c_in.getValueBits();
+        value = a.getValue() - b.getValue() - c_in.getValue();
     }
 }
diff --git a/src/main/java/de/neemann/digital/core/wiring/Multiplexer.java b/src/main/java/de/neemann/digital/core/wiring/Multiplexer.java
index 793517df3..a6ab96881 100644
--- a/src/main/java/de/neemann/digital/core/wiring/Multiplexer.java
+++ b/src/main/java/de/neemann/digital/core/wiring/Multiplexer.java
@@ -23,7 +23,7 @@ public class Multiplexer extends FanIn {
 
     @Override
     public void readInputs() throws NodeException {
-        int n = (int) selector.getValueBits();
+        int n = (int) selector.getValue();
         if (n >= inputs.size())
             throw new NodeException("multiplexerSelectsNotPresentInput");
 
diff --git a/src/main/java/de/neemann/digital/gui/Main.java b/src/main/java/de/neemann/digital/gui/Main.java
index 33d1597d1..24f39033b 100644
--- a/src/main/java/de/neemann/digital/gui/Main.java
+++ b/src/main/java/de/neemann/digital/gui/Main.java
@@ -19,16 +19,20 @@ import de.process.utils.gui.ErrorMessage;
 import de.process.utils.gui.ToolTipAction;
 
 import javax.swing.*;
+import javax.swing.filechooser.FileNameExtensionFilter;
 import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.io.File;
+import java.io.FileReader;
 import java.io.FileWriter;
 import java.io.IOException;
+import java.util.prefs.Preferences;
 
 /**
  * @author hneemann
  */
 public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
+    private static final Preferences prefs = Preferences.userRoot().node("dig");
     private final CircuitComponent circuitComponent;
     private final InsertHistory insertHistory;
     private final ToolTipAction save;
@@ -40,6 +44,11 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
 
         Circuit cr = new Circuit();
         circuitComponent = new CircuitComponent(cr);
+        String name = prefs.get("name", null);
+        if (name != null) {
+            loadFile(new File(name));
+        }
+
         getContentPane().add(circuitComponent);
 
         addWindowListener(new ClosingWindowListener(this, this));
@@ -54,14 +63,17 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
         ToolTipAction open = new ToolTipAction("Open") {
             @Override
             public void actionPerformed(ActionEvent e) {
-
+                JFileChooser fc = getjFileChooser();
+                if (fc.showOpenDialog(Main.this) == JFileChooser.APPROVE_OPTION) {
+                    loadFile(fc.getSelectedFile());
+                }
             }
         };
 
         ToolTipAction saveas = new ToolTipAction("Save As") {
             @Override
             public void actionPerformed(ActionEvent e) {
-                JFileChooser fc = new JFileChooser(filename == null ? null : filename.getParentFile());
+                JFileChooser fc = getjFileChooser();
                 if (fc.showSaveDialog(Main.this) == JFileChooser.APPROVE_OPTION) {
                     saveFile(fc.getSelectedFile());
                 }
@@ -113,7 +125,7 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
             @Override
             public void actionPerformed(ActionEvent e) {
                 try {
-                    ModelDescription m = new ModelDescription(cr);
+                    ModelDescription m = new ModelDescription(circuitComponent.getCircuit());
                     Model model = m.create(circuitComponent);
                     model.init(true);
                     circuitComponent.setMode(CircuitComponent.Mode.running);
@@ -143,6 +155,20 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
         SwingUtilities.invokeLater(() -> new Main().setVisible(true));
     }
 
+    private static XStream getxStream() {
+        XStream xStream = new XStream(new StaxDriver());
+        xStream.alias("visualPart", VisualPart.class);
+        xStream.alias("wire", Wire.class);
+        xStream.alias("circuit", Circuit.class);
+        return xStream;
+    }
+
+    private JFileChooser getjFileChooser() {
+        JFileChooser fileChooser = new JFileChooser(filename == null ? null : filename.getParentFile());
+        fileChooser.addChoosableFileFilter(new FileNameExtensionFilter("Circuit", "dig"));
+        return fileChooser;
+    }
+
     @Override
     public boolean isStateChanged() {
         return false;
@@ -153,14 +179,30 @@ public class Main extends JFrame implements ClosingWindowListener.ConfirmSave {
         save.actionPerformed(null);
     }
 
-    private void saveFile(File filename) {
-        XStream xStream = new XStream(new StaxDriver());
-        xStream.alias("visualPart", VisualPart.class);
-        xStream.alias("wire", Wire.class);
-        xStream.alias("circuit", Circuit.class);
+    private void loadFile(File filename) {
+        XStream xStream = getxStream();
+        try (FileReader in = new FileReader(filename)) {
+            circuitComponent.setCircuit((Circuit) xStream.fromXML(in));
+            setFilename(filename);
+        } catch (IOException e) {
+            new ErrorMessage("error writing a file").addCause(e).show();
+        }
+    }
 
+    private void setFilename(File filename) {
+        this.filename = filename;
+        prefs.put("name", filename.getPath());
+        setTitle(filename + " - Digital");
+    }
+
+    private void saveFile(File filename) {
+        if (!filename.getName().endsWith(".dig"))
+            filename = new File(filename.getPath() + ".dig");
+
+        XStream xStream = getxStream();
         try (FileWriter out = new FileWriter(filename)) {
             xStream.marshal(circuitComponent.getCircuit(), new PrettyPrintWriter(out));
+            setFilename(filename);
         } catch (IOException e) {
             new ErrorMessage("error writing a file").addCause(e).show();
         }
diff --git a/src/main/java/de/neemann/digital/gui/components/CircuitComponent.java b/src/main/java/de/neemann/digital/gui/components/CircuitComponent.java
index 9f13c3dcc..09cb4f0a7 100644
--- a/src/main/java/de/neemann/digital/gui/components/CircuitComponent.java
+++ b/src/main/java/de/neemann/digital/gui/components/CircuitComponent.java
@@ -23,11 +23,11 @@ import java.util.ArrayList;
 public class CircuitComponent extends JComponent implements Listener {
 
     private static final String delAction = "myDelAction";
-    private final Circuit circuit;
+    private Circuit circuit;
     private Mouse listener;
 
-    public CircuitComponent(Circuit circuit) {
-        this.circuit = circuit;
+    public CircuitComponent(Circuit aCircuit) {
+        this.circuit = aCircuit;
         setMode(Mode.part);
 
         KeyStroke delKey = KeyStroke.getKeyStroke("DELETE");
@@ -35,7 +35,6 @@ public class CircuitComponent extends JComponent implements Listener {
         getActionMap().put(delAction, new AbstractAction() {
             @Override
             public void actionPerformed(ActionEvent e) {
-                System.out.println("write");
                 if (listener instanceof SelectMouseListener) {
                     SelectMouseListener mml = (SelectMouseListener) listener;
                     if (mml.corner1 != null && mml.corner2 != null) {
@@ -110,6 +109,11 @@ public class CircuitComponent extends JComponent implements Listener {
         return circuit;
     }
 
+    public void setCircuit(Circuit circuit) {
+        this.circuit = circuit;
+        setMode(Mode.part);
+    }
+
     public enum Mode {part, wire, running, select}
 
     private interface Mouse extends MouseMotionListener, MouseListener {
diff --git a/src/main/java/de/neemann/digital/gui/draw/graphics/Style.java b/src/main/java/de/neemann/digital/gui/draw/graphics/Style.java
index 786865be7..6534dd3e8 100644
--- a/src/main/java/de/neemann/digital/gui/draw/graphics/Style.java
+++ b/src/main/java/de/neemann/digital/gui/draw/graphics/Style.java
@@ -7,8 +7,8 @@ import java.awt.*;
  */
 public class Style {
     public static final Style NORMAL = new Style(2, false, Color.BLACK);
-    public static final Style WIRE = new Style(2, true, Color.BLUE);
-    public static final Style WIRE_HIGH = new Style(2, true, new Color(0, 153, 255));
+    public static final Style WIRE = new Style(3, true, new Color(0, 112, 0));
+    public static final Style WIRE_HIGH = new Style(3, true, new Color(102, 255, 102));
     public static final Style FILLED = new Style(2, true, Color.BLACK);
     public static final Style THIN = new Style(1, false, Color.BLACK);
 
diff --git a/src/main/java/de/neemann/digital/gui/draw/model/Net.java b/src/main/java/de/neemann/digital/gui/draw/model/Net.java
index 1f2d9e2c3..47379432d 100644
--- a/src/main/java/de/neemann/digital/gui/draw/model/Net.java
+++ b/src/main/java/de/neemann/digital/gui/draw/model/Net.java
@@ -16,20 +16,25 @@ public class Net {
 
     private final HashSet<Vector> points;
     private final ArrayList<Pin> pins;
+    private final ArrayList<Wire> wires;
 
     public Net(Wire w) {
         points = new HashSet<>();
         points.add(w.p1);
         points.add(w.p2);
         pins = new ArrayList<>();
+        wires = new ArrayList<>();
+        wires.add(w);
     }
 
     public Vector tryMerge(Wire wire) {
         if (points.contains(wire.p1)) {
+            wires.add(wire);
             points.add(wire.p2);
             return wire.p2;
         }
         if (points.contains(wire.p2)) {
+            wires.add(wire);
             points.add(wire.p1);
             return wire.p1;
         }
@@ -42,6 +47,7 @@ public class Net {
 
     public void addAllPointsFrom(Net changedNet) {
         points.addAll(changedNet.points);
+        wires.addAll(changedNet.wires);
     }
 
     public void add(Pin pin) {
@@ -71,5 +77,9 @@ public class Net {
         for (Pin i : inputs) {
             i.setValue(value);
         }
+
+        for (Wire w : wires)
+            w.setValue(value);
+
     }
 }
diff --git a/src/main/java/de/neemann/digital/gui/draw/parts/Circuit.java b/src/main/java/de/neemann/digital/gui/draw/parts/Circuit.java
index 056733699..cebb05af7 100644
--- a/src/main/java/de/neemann/digital/gui/draw/parts/Circuit.java
+++ b/src/main/java/de/neemann/digital/gui/draw/parts/Circuit.java
@@ -12,7 +12,7 @@ import java.util.Iterator;
  * @author hneemann
  */
 public class Circuit implements Drawable {
-    private static final Vector RAD = new Vector(2, 2);
+    private static final Vector RAD = new Vector(3, 3);
     private final ArrayList<VisualPart> visualParts;
     private transient ArrayList<Vector> dots;
     private ArrayList<Wire> wires;
@@ -25,10 +25,10 @@ public class Circuit implements Drawable {
 
     @Override
     public void drawTo(Graphic graphic, State state) {
+        for (Vector d : getDots())
+            graphic.drawCircle(d.sub(RAD), d.add(RAD), Style.WIRE);
         for (Wire w : wires)
             w.drawTo(graphic, state);
-        for (Vector d : dots)
-            graphic.drawCircle(d.sub(RAD), d.add(RAD), Style.WIRE);
         for (VisualPart p : visualParts)
             p.drawTo(graphic, state);
     }
@@ -56,7 +56,7 @@ public class Circuit implements Drawable {
         wires.add(newWire);
         WireConsistencyChecker checker = new WireConsistencyChecker(wires);
         wires = checker.check();
-        dots = WireConsistencyChecker.createDots(wires);
+        dots = null;
     }
 
     public ArrayList<VisualPart> getParts() {
@@ -99,4 +99,10 @@ public class Circuit implements Drawable {
     public ArrayList<Wire> getWires() {
         return wires;
     }
+
+    public ArrayList<Vector> getDots() {
+        if (dots == null)
+            dots = WireConsistencyChecker.createDots(wires);
+        return dots;
+    }
 }
diff --git a/src/main/java/de/neemann/digital/gui/draw/parts/Wire.java b/src/main/java/de/neemann/digital/gui/draw/parts/Wire.java
index e814eb758..542803499 100644
--- a/src/main/java/de/neemann/digital/gui/draw/parts/Wire.java
+++ b/src/main/java/de/neemann/digital/gui/draw/parts/Wire.java
@@ -1,5 +1,6 @@
 package de.neemann.digital.gui.draw.parts;
 
+import de.neemann.digital.core.ObservableValue;
 import de.neemann.digital.gui.draw.graphics.Graphic;
 import de.neemann.digital.gui.draw.graphics.Style;
 import de.neemann.digital.gui.draw.graphics.Vector;
@@ -12,6 +13,7 @@ public class Wire implements Drawable, Moveable {
 
     public Vector p1;
     public Vector p2;
+    private ObservableValue value;
 
     public Wire(Vector p1, Vector p2) {
         this.p1 = p1;
@@ -20,7 +22,12 @@ public class Wire implements Drawable, Moveable {
 
     @Override
     public void drawTo(Graphic graphic, State state) {
-        graphic.drawLine(p1, p2, Style.WIRE);
+        Style style = Style.WIRE;
+        if (value != null && value.getValue() != 0) {
+            style = Style.WIRE_HIGH;
+        }
+
+        graphic.drawLine(p1, p2, style);
     }
 
     @Override
@@ -77,5 +84,9 @@ public class Wire implements Drawable, Moveable {
                 '}';
     }
 
+    public void setValue(ObservableValue value) {
+        this.value = value;
+    }
+
     enum Orientation {horzontal, vertical, diagonal}
 }
diff --git a/src/main/java/de/neemann/digital/gui/draw/shapes/GenericShape.java b/src/main/java/de/neemann/digital/gui/draw/shapes/GenericShape.java
index 91f2a4e9f..69e398ddd 100644
--- a/src/main/java/de/neemann/digital/gui/draw/shapes/GenericShape.java
+++ b/src/main/java/de/neemann/digital/gui/draw/shapes/GenericShape.java
@@ -76,6 +76,21 @@ public class GenericShape implements Shape {
 
     @Override
     public Interactor applyStateMonitor(State state, Listener listener, Model model) {
+        if (symmetric) {
+            state.getOutput(0).addListener(new Listener() {
+                public long lastValue = 0;
+
+                @Override
+                public void needsUpdate() {
+                    long value = state.getInput(0).getValue();
+                    if (lastValue != value) {
+                        lastValue = value;
+                        listener.needsUpdate();
+                    }
+                }
+            });
+
+        }
         return null;
     }
 
@@ -84,6 +99,11 @@ public class GenericShape implements Shape {
         int max = Math.max(inputs, outputs);
         int height = (max - 1) * SIZE + SIZE2;
 
+        if (symmetric && state != null) {
+            graphic.drawText(new Vector(width * SIZE, 0), new Vector((width + 1) * SIZE, 0), Long.toString(state.getOutput(0).getValue()));
+        }
+
+
         if (symmetric && ((inputs & 1) == 0)) height += SIZE;
 
         graphic.drawPolygon(new Polygon(true)
diff --git a/src/test/java/de/neemann/digital/FlipFlops.java b/src/test/java/de/neemann/digital/FlipFlops.java
index 401f20967..914ec23f9 100644
--- a/src/test/java/de/neemann/digital/FlipFlops.java
+++ b/src/test/java/de/neemann/digital/FlipFlops.java
@@ -32,8 +32,8 @@ public class FlipFlops extends TestCase {
         s.setValue(0);
         model.doStep(true);     // geht nur mit noise!
 
-        assertTrue((a1.getOutput().getValueBits() == 1 && a2.getOutput().getValueBits() == 0) ||  // endzustand ist undefiniert!
-                (a1.getOutput().getValueBits() == 0 && a2.getOutput().getValueBits() == 1));
+        assertTrue((a1.getOutput().getValue() == 1 && a2.getOutput().getValue() == 0) ||  // endzustand ist undefiniert!
+                (a1.getOutput().getValue() == 0 && a2.getOutput().getValue() == 1));
     }
 
     public void testFlipFlopNAnd() throws Exception {
diff --git a/src/test/java/de/neemann/digital/TestExecuter.java b/src/test/java/de/neemann/digital/TestExecuter.java
index 64b50d795..743affc59 100644
--- a/src/test/java/de/neemann/digital/TestExecuter.java
+++ b/src/test/java/de/neemann/digital/TestExecuter.java
@@ -43,7 +43,7 @@ public class TestExecuter {
         for (int i = 0; i < outputs.length; i++) {
             int should = val[i + inputs.length];
             if (should >= 0)
-                assertEquals("output " + i, outputs[i].getValueBits(should), outputs[i].getValueBits());
+                assertEquals("output " + i, outputs[i].getValueBits(should), outputs[i].getValue());
         }
     }