diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Add.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Add.java
deleted file mode 100644
index d557740..0000000
--- a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Add.java
+++ /dev/null
@@ -1,23 +0,0 @@
-package de.uulm.sp.swt.profcalculator;
-
-public class Add {
-	
-	public Value l, r;
-
-	public Add(Value l, Value r) {
-		this.l = l;
-		this.r = r;
-	}
-
-	public String toString() {
-		return l.toString() + " + " + r.toString();
-	}
-
-	public int evaluate() {
-		return l.getValue() + r.getValue();
-	}
-
-	public String computeEquation() {
-		return toString() + " = " + evaluate();
-	}
-}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Logger.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Logger.java
new file mode 100644
index 0000000..8786ac8
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Logger.java
@@ -0,0 +1,23 @@
+package de.uulm.sp.swt.profcalculator;
+
+public class Logger {
+	
+	public static final boolean LOGGING = true;
+	
+	private static Logger logger = new Logger();
+
+	private Logger() {
+		log("Logging enabled");
+	}
+
+	public void log(String message) {
+		if (LOGGING) {
+			System.out.println(message);
+		}
+	}
+	
+	public static Logger getLogger() {
+		return logger;
+	}
+
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Observer.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Observer.java
new file mode 100644
index 0000000..9d01f2d
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Observer.java
@@ -0,0 +1,5 @@
+package de.uulm.sp.swt.profcalculator;
+
+public interface Observer {
+	void update();
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/ProfCalculator.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/ProfCalculator.java
index 0e2930e..9ccbfa7 100644
--- a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/ProfCalculator.java
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/ProfCalculator.java
@@ -1,5 +1,14 @@
 package de.uulm.sp.swt.profcalculator;
 
+import de.uulm.sp.swt.profcalculator.expressions.Addition;
+import de.uulm.sp.swt.profcalculator.expressions.CounterValue;
+import de.uulm.sp.swt.profcalculator.expressions.CounterValue;
+import de.uulm.sp.swt.profcalculator.expressions.Expression;
+import de.uulm.sp.swt.profcalculator.expressions.Multiplication;
+import de.uulm.sp.swt.profcalculator.expressions.NecessaryBrackets;
+import de.uulm.sp.swt.profcalculator.expressions.Value;
+import de.uulm.sp.swt.profcalculator.gui.BlueFontGUIFactory;
+import de.uulm.sp.swt.profcalculator.gui.GUIFactory;
 import javafx.application.Application;
 import javafx.event.ActionEvent;
 import javafx.event.EventHandler;
@@ -12,32 +21,34 @@
 import javafx.scene.paint.Color;
 import javafx.stage.Stage;
 
-public class ProfCalculator	extends Application implements EventHandler<ActionEvent> {
+public class ProfCalculator	extends Application implements EventHandler<ActionEvent>, Observer {
 
-	private final static Value DEFAULT_VALUE = new Value(0);
+	private Expression expression = new CounterValue(this);
+	
+	private GUIFactory guiFactory = new BlueFontGUIFactory();
 
-	private Add addition = new Add(DEFAULT_VALUE, DEFAULT_VALUE);
-
-	private Label errorLabel = new Label();
+	private Label errorLabel = guiFactory.createLabel();
 
 	private TextField inputField = new TextField();
 
-	private Button addButton = new Button("+");
+	private Button additionButton = guiFactory.createButton("+");
+	private Button multiplicationButton = guiFactory.createButton("*");
 
-	private Label resultLabel = new Label();
+	private Label resultLabel = guiFactory.createLabel();
 
 	@Override
 	public void start(Stage stage) throws Exception {
 		stage.setTitle("Professorial Calculator");
 		errorLabel.setTextFill(Color.web("#AA0000"));
 
-		VBox layout = new VBox(10, errorLabel, inputField, addButton, resultLabel);
+		VBox layout = new VBox(10, errorLabel, inputField, additionButton, multiplicationButton, resultLabel);
 		layout.setPadding(new Insets(20, 80, 20, 80));
 		Scene scene = new Scene(layout);
 
 		stage.setScene(scene);
 		stage.show();
-		addButton.setOnAction(this);
+		additionButton.setOnAction(this);
+		multiplicationButton.setOnAction(this);
 		updateGUI();
 	}
 
@@ -45,8 +56,15 @@ public void start(Stage stage) throws Exception {
 	public void handle(ActionEvent event) {
 		try {
 			int newValue = Integer.parseInt(inputField.getText());
-			int oldResult = addition.evaluate();
-			addition = new Add(new Value(oldResult), new Value(newValue));
+			if (event.getSource() == additionButton) {
+				expression = new Addition(expression, new Value(newValue));
+				Logger.getLogger().log("+ " + newValue);
+			}
+			else if (event.getSource() == multiplicationButton) {
+				expression = new Multiplication(expression, new Value(newValue));
+				Logger.getLogger().log("* " + newValue);
+			}
+			expression = new NecessaryBrackets(expression);
 			updateGUI();
 			inputField.requestFocus();
 		} catch (NumberFormatException e) {
@@ -54,8 +72,8 @@ public void handle(ActionEvent event) {
 		}
 	}
 
-	private void updateGUI() {
-		resultLabel.setText(addition.computeEquation());
+	public void updateGUI() {
+		resultLabel.setText(expression.computeEquation());
 		inputField.setText("");
 		errorLabel.setText("");
 	}
@@ -64,4 +82,9 @@ public static void main(String[] args) {
 		launch(args);
 	}
 
+	@Override
+	public void update() {
+		updateGUI();
+	}
+
 }
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Subject.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Subject.java
new file mode 100644
index 0000000..dabadaf
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Subject.java
@@ -0,0 +1,7 @@
+package de.uulm.sp.swt.profcalculator;
+
+public interface Subject {
+	void register(Observer observer);
+	void unregister(Observer observer);
+	void notifyObservers();
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Value.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Value.java
deleted file mode 100644
index 85e75c7..0000000
--- a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/Value.java
+++ /dev/null
@@ -1,18 +0,0 @@
-package de.uulm.sp.swt.profcalculator;
-
-public class Value {
-
-	Integer value;
-
-	public Value(int value) {
-		this.value = value;
-	}
-
-	public String toString() {
-		return value.toString();
-	}
-
-	public int getValue() {
-		return value.intValue();
-	}
-}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Addition.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Addition.java
new file mode 100644
index 0000000..290f903
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Addition.java
@@ -0,0 +1,21 @@
+package de.uulm.sp.swt.profcalculator.expressions;
+
+public class Addition extends Expression {
+	
+	public Expression left;
+	public Expression right;
+
+	public Addition(Expression left, Expression right) {
+		this.left = left;
+		this.right = right;
+	}
+
+	public String toString(Expression parent) {
+		return left.toString(this) + " + " + right.toString(this);
+	}
+
+	public int evaluate() {
+		return left.evaluate() + right.evaluate();
+	}
+	
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/CounterValue.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/CounterValue.java
new file mode 100644
index 0000000..3b402ae
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/CounterValue.java
@@ -0,0 +1,54 @@
+package de.uulm.sp.swt.profcalculator.expressions;
+
+import java.util.LinkedList;
+
+import de.uulm.sp.swt.profcalculator.Observer;
+import de.uulm.sp.swt.profcalculator.ProfCalculator;
+import de.uulm.sp.swt.profcalculator.Subject;
+import javafx.application.Platform;
+
+public class CounterValue extends Value implements Runnable, Subject {
+	
+	private LinkedList<Observer> observerList = new LinkedList<Observer>();
+
+	public CounterValue(ProfCalculator calc) {
+		super(0);
+		observerList.add(calc);
+		new Thread(this).start();
+	}
+
+	@Override
+	public void run() {
+		while (value < 10) {
+			try {
+				Thread.sleep(1000);
+			} catch (InterruptedException e) {
+			}
+			value++;
+			Platform.runLater(new Runnable() {
+				@Override
+				public void run() {
+					notifyObservers();
+				}
+			});
+		}
+	}
+
+	@Override
+	public void register(Observer observer) {
+		observerList.add(observer);
+	}
+
+	@Override
+	public void unregister(Observer observer) {
+		observerList.remove(observer);
+	}
+
+	@Override
+	public void notifyObservers() {
+		for(int i=0;i<observerList.size();i++) {
+			observerList.get(i).update();
+		}
+	}
+
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Expression.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Expression.java
new file mode 100644
index 0000000..2047d49
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Expression.java
@@ -0,0 +1,17 @@
+package de.uulm.sp.swt.profcalculator.expressions;
+
+public abstract class Expression {
+
+	public abstract int evaluate();
+
+	public abstract String toString(Expression parent);
+
+	public String toString() {
+		return toString(null);
+	}
+
+	public String computeEquation() {
+		return toString() + " = " + evaluate();
+	}
+
+}
\ No newline at end of file
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Multiplication.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Multiplication.java
new file mode 100644
index 0000000..7256be3
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Multiplication.java
@@ -0,0 +1,21 @@
+package de.uulm.sp.swt.profcalculator.expressions;
+
+public class Multiplication extends Expression {
+
+	public Expression left;
+	public Expression right;
+
+	public Multiplication(Expression left, Expression right) {
+		this.left = left;
+		this.right = right;
+	}
+
+	public String toString(Expression parent) {
+		return left.toString(this) + " * " + right.toString(this);
+	}
+
+	public int evaluate() {
+		return left.evaluate() * right.evaluate();
+	}
+	
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/NecessaryBrackets.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/NecessaryBrackets.java
new file mode 100644
index 0000000..177b051
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/NecessaryBrackets.java
@@ -0,0 +1,25 @@
+package de.uulm.sp.swt.profcalculator.expressions;
+
+public class NecessaryBrackets extends Expression {
+
+	private Expression expression;
+
+	public NecessaryBrackets(Expression expression) {
+		this.expression = expression;
+	}
+	
+	@Override
+	public String toString(Expression parent) {
+		String childString = expression.toString(parent);
+		if (parent instanceof Multiplication && expression instanceof Addition) {
+			childString = "(" + childString + ")";
+		}
+		return childString;
+	}
+
+	@Override
+	public int evaluate() {
+		return expression.evaluate();
+	}
+
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Value.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Value.java
new file mode 100644
index 0000000..c9f9ed6
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/expressions/Value.java
@@ -0,0 +1,20 @@
+package de.uulm.sp.swt.profcalculator.expressions;
+
+public class Value extends Expression {
+
+	Integer value;
+
+	public Value(int value) {
+		this.value = value;
+	}
+
+	public String toString(Expression parent) {
+		return value.toString();
+	}
+
+	@Override
+	public int evaluate() {
+		return value.intValue();
+	}
+
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/BlueFontGUIFactory.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/BlueFontGUIFactory.java
new file mode 100644
index 0000000..2895784
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/BlueFontGUIFactory.java
@@ -0,0 +1,26 @@
+package de.uulm.sp.swt.profcalculator.gui;
+
+import javafx.scene.control.Button;
+import javafx.scene.control.Label;
+import javafx.scene.paint.Color;
+import javafx.scene.text.Font;
+
+public class BlueFontGUIFactory implements GUIFactory {
+	
+	final static Color BLUE = Color.web("#0000AA");
+	
+	@Override
+	public Label createLabel() {
+		Label label = new Label();
+		label.setTextFill(BLUE);
+		return label;
+	}
+
+	@Override
+	public Button createButton(String title) {
+		Button button = new Button(title);
+		button.setTextFill(BLUE);
+		return button;
+	}
+
+}
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/GUIFactory.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/GUIFactory.java
new file mode 100644
index 0000000..146d358
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/GUIFactory.java
@@ -0,0 +1,12 @@
+package de.uulm.sp.swt.profcalculator.gui;
+
+import javafx.scene.control.Button;
+import javafx.scene.control.Label;
+
+public interface GUIFactory {
+
+	Label createLabel();
+
+	Button createButton(String title);
+
+}
\ No newline at end of file
diff --git a/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/LargeFontGUIFactory.java b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/LargeFontGUIFactory.java
new file mode 100644
index 0000000..f482bb3
--- /dev/null
+++ b/ProfCalculator/src/de/uulm/sp/swt/profcalculator/gui/LargeFontGUIFactory.java
@@ -0,0 +1,25 @@
+package de.uulm.sp.swt.profcalculator.gui;
+
+import javafx.scene.control.Button;
+import javafx.scene.control.Label;
+import javafx.scene.text.Font;
+
+public class LargeFontGUIFactory implements GUIFactory {
+	
+	final static Font FONT = new Font("Arial", 24);
+	
+	@Override
+	public Label createLabel() {
+		Label label = new Label();
+		label.setFont(FONT);
+		return label;
+	}
+
+	@Override
+	public Button createButton(String title) {
+		Button button = new Button(title);
+		button.setFont(FONT);
+		return button;
+	}
+
+}