diff --git a/src/de/itstall/TaschenrechnerGui.java b/src/de/itstall/TaschenrechnerGui.java
index 8fc2cd5938538eb0ad3ad17997a3f5f022bf4aec..c6e8fe4b3a2b69ac5e174e6ab0f8613d5581ebf7 100644
--- a/src/de/itstall/TaschenrechnerGui.java
+++ b/src/de/itstall/TaschenrechnerGui.java
@@ -119,13 +119,14 @@ public class TaschenrechnerGui extends JFrame {
 		this.setTitle("Taschenrechner");
 		this.setSize(300, 200);
 		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
-		this.setResizable(false);
+		this.setResizable(true);
 
 		panel = new JPanel();
 		panel.setLayout(new GridLayout(4, 5));
 
 		txtCalculation.setBounds(20, 20, 260, 20);
 		txtCalculation.setHorizontalAlignment(JTextField.RIGHT);
+		txtCalculation.setEditable(false);
 		this.add(txtCalculation, BorderLayout.PAGE_START);
 
 		ActionListener insert = new InsertAction();
@@ -175,13 +176,15 @@ public class TaschenrechnerGui extends JFrame {
 			strDisplay = strDisplay.replace("--", "-");
 			strDisplay = strDisplay.replace("-+-", "-");
 			strDisplay = strDisplay.replace("+-+", "+");
+			strDisplay = strDisplay.replace("NaN", "");
 		}
 
 		return strDisplay;
 	}
 
 	private void calculate() {
-		txtCalculation.setText("= " + berechnen(txtCalculation.getText()));
+		String txtCalc = replaceSigns(txtCalculation.getText());
+		txtCalculation.setText("= " + berechnen(txtCalc));
 	}
 
 	private void clearDisplay() {