diff --git a/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f2..f2cf94a 100644
--- a/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -14,6 +14,7 @@ public class Calculator {
 
     private String latestOperation = "";
 
+    private boolean clearPressedOnce = false; //  Neue Ergänzung
     /**
      * @return den aktuellen Bildschirminhalt als String
      */
@@ -44,12 +45,24 @@ public void pressDigitKey(int digit) {
      * Werte sowie der aktuelle Operationsmodus zurückgesetzt, so dass der Rechner wieder
      * im Ursprungszustand ist.
      */
-    public void pressClearKey() {
+    
+    /**public void pressClearKey() {
         screen = "0";
         latestOperation = "";
         latestValue = 0.0;
+    }*/
+    
+        public void pressClearKey() {
+        if (!clearPressedOnce) {
+            screen = "0";                  // nur den Bildschirm löschen
+            clearPressedOnce = true;       // nur einmal gedrückt
+        } else {
+            screen = "0";                  // sonst kompletter Reset
+            latestOperation = "";
+            latestValue = 0.0;
+            clearPressedOnce = false;      // zurücksetzen
+        }
     }
-
     /**
      * Empfängt den Wert einer gedrückten binären Operationstaste, also eine der vier Operationen
      * Addition, Substraktion, Division, oder Multiplikation, welche zwei Operanden benötigen.
@@ -77,7 +90,11 @@ public void pressUnaryOperationKey(String operation) {
         var result = switch(operation) {
             case "√" -> Math.sqrt(Double.parseDouble(screen));
             case "%" -> Double.parseDouble(screen) / 100;
-            case "1/x" -> 1 / Double.parseDouble(screen);
+            //case "1/x" -> 1 / Double.parseDouble(screen);
+            case "1/x" -> {
+            if (Double.parseDouble(screen) == 0) yield Double.NaN;
+            else yield 1 / Double.parseDouble(screen);
+            }
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
diff --git a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
index ddff0da..05f643c 100644
--- a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -90,5 +90,52 @@ void testMultipleDecimalDots() {
 
 
     //TODO hier weitere Tests erstellen
+
+    @Test
+    @DisplayName("should correctly calculate percent")
+    void testPercentOperation() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("%");
+
+        String expected = "0.5";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should not reset memory on first clear press")
+    void testClearKeyOnce() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(4);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(5);
+        calc.pressClearKey();
+        calc.pressDigitKey(2);
+        calc.pressEqualsKey();
+
+        String expected = "6";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should display error when inverting zero")
+    void testInversionOfZero() {
+        Calculator calc = new Calculator();
+    
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("1/x");
+    
+        String expected = "Error";
+        String actual = calc.readScreen();
+    
+        assertEquals(expected, actual);
+    }
 }