diff --git a/src/main/java/de/neemann/digital/analyse/DependencyAnalyser.java b/src/main/java/de/neemann/digital/analyse/DependencyAnalyser.java
index 6858b82f3..0cc150693 100644
--- a/src/main/java/de/neemann/digital/analyse/DependencyAnalyser.java
+++ b/src/main/java/de/neemann/digital/analyse/DependencyAnalyser.java
@@ -52,7 +52,7 @@ public class DependencyAnalyser {
         if (!effected.contains(value)) {
             effected.add(value);
 
-            for (Observer o : value) {
+            for (Observer o : value.getObservers()) {
                 if ((o instanceof NodeInterface)) {
                     ObservableValues outputs = ((NodeInterface) o).getOutputs();
                     for (ObservableValue co : outputs)
diff --git a/src/main/java/de/neemann/digital/core/Observable.java b/src/main/java/de/neemann/digital/core/Observable.java
index 99da67c6a..96596f20b 100644
--- a/src/main/java/de/neemann/digital/core/Observable.java
+++ b/src/main/java/de/neemann/digital/core/Observable.java
@@ -8,7 +8,7 @@ import java.util.Iterator;
  *
  * @author hneemann
  */
-public class Observable implements Iterable<Observer> {
+public class Observable {
     private final ArrayList<Observer> observers;
 
     /**
@@ -76,8 +76,11 @@ public class Observable implements Iterable<Observer> {
         return observers.contains(observer);
     }
 
-    @Override
-    public Iterator<Observer> iterator() {
-        return observers.iterator();
+    /**
+     * @return tje list of observers
+     */
+    public ArrayList<Observer> getObservers() {
+        return observers;
     }
+
 }
diff --git a/src/main/java/de/neemann/digital/data/ValueTable.java b/src/main/java/de/neemann/digital/data/ValueTable.java
index 66571f84f..e211a8ca2 100644
--- a/src/main/java/de/neemann/digital/data/ValueTable.java
+++ b/src/main/java/de/neemann/digital/data/ValueTable.java
@@ -1,5 +1,7 @@
 package de.neemann.digital.data;
 
+import de.neemann.digital.core.Observable;
+
 import java.io.*;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -9,7 +11,7 @@ import java.util.Iterator;
  * Stores values in a table
  * Created by hneemann on 03.07.17.
  */
-public class ValueTable implements Iterable<Value[]> {
+public class ValueTable extends Observable implements Iterable<Value[]> {
 
     private final String[] names;
     private final ArrayList<Value[]> values;
@@ -59,6 +61,9 @@ public class ValueTable implements Iterable<Value[]> {
         }
         values.add(row);
         checkMax(row);
+
+        fireHasChanged();
+
         return this;
     }
 
@@ -151,6 +156,7 @@ public class ValueTable implements Iterable<Value[]> {
     public void clear() {
         values.clear();
         Arrays.fill(max, 0);
+        fireHasChanged();
     }
 
     /**