diff --git a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f21..fc09d0f2 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -33,7 +33,9 @@ public void pressDigitKey(int digit) {
 
         if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
 
+        if (screen.length() < 10) { //Durch Hinzufügen der Bedingung if (screen.length() < 10) stellen wir sicher, dass Ziffern nur dann dem Bildschirm hinzugefügt werden, wenn die maximale Länge noch nicht erreicht ist.
         screen = screen + digit;
+        }
     }
 
     /**
@@ -74,18 +76,21 @@ public void pressBinaryOperationKey(String operation)  {
     public void pressUnaryOperationKey(String operation) {
         latestValue = Double.parseDouble(screen);
         latestOperation = operation;
-        var result = switch(operation) {
-            case "√" -> Math.sqrt(Double.parseDouble(screen));
-            case "%" -> Double.parseDouble(screen) / 100;
-            case "1/x" -> 1 / Double.parseDouble(screen);
-            default -> throw new IllegalArgumentException();
-        };
-        screen = Double.toString(result);
-        if(screen.equals("NaN")) screen = "Error";
-        if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
-
+        if (latestValue == 0 && operation.equals("1/x")) { //Durch Hinzufügen der Bedingung if (latestValue == 0 && operation.equals("1/x")) überprüfen wir, ob der zu invertierende Wert Null ist. In diesem Fall setzen wir den Bildschirm auf "Error".
+            screen = "Error";
+        } else {
+            var result = switch(operation) {
+                case "√" -> Math.sqrt(Double.parseDouble(screen));
+                case "%" -> Double.parseDouble(screen) / 100;
+                case "1/x" -> 1 / Double.parseDouble(screen);
+                default -> throw new IllegalArgumentException();
+            };
+            screen = Double.toString(result);
+            if(screen.equals("NaN")) screen = "Error";
+            if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
+        }
     }
-
+    
     /**
      * Empfängt den Befehl der gedrückten Dezimaltrennzeichentaste, im Englischen üblicherweise "."
      * Fügt beim ersten Mal Drücken dem aktuellen Bildschirminhalt das Trennzeichen auf der rechten
diff --git a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
index ddff0daf..1c55c166 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -89,6 +89,57 @@ void testMultipleDecimalDots() {
     }
 
 
-    //TODO hier weitere Tests erstellen
+//Teilaufgabe 1
+    @Test
+    @DisplayName("should display result after pressing the clear key once")
+    void testPressClearKeyOnce() {
+        Calculator calc = new Calculator();
+    
+        calc.pressDigitKey(5);
+        calc.pressClearKey();
+    
+        String expected = "0";
+        String actual = calc.readScreen();
+    
+        assertEquals(expected, actual);
+    }
+//Teilaufgabe 2
+    @Test
+    @DisplayName("should display error when trying to invert zero")
+    void testInvertingZero() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("1/x");
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should display error when exceeding maximum screen capacity")
+    void testMaxScreenCapacity() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(2);
+        calc.pressDigitKey(3);
+        calc.pressDigitKey(4);
+        calc.pressDigitKey(5);
+        calc.pressDigitKey(6);
+        calc.pressDigitKey(7);
+        calc.pressDigitKey(8);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(1); // sollte ignoriert werden
+
+        String expected = "1234567890";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
 }