diff --git a/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f2..bfffe67 100644
--- a/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -14,6 +14,9 @@ public class Calculator {
 
     private String latestOperation = "";
 
+    private boolean wasClearedOnce = false;
+
+
     /**
      * @return den aktuellen Bildschirminhalt als String
      */
@@ -31,11 +34,14 @@ public String readScreen() {
     public void pressDigitKey(int digit) {
         if(digit > 9 || digit < 0) throw new IllegalArgumentException();
 
+        wasClearedOnce = false;
+
         if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
 
         screen = screen + digit;
     }
 
+
     /**
      * Empfängt den Befehl der C- bzw. CE-Taste (Clear bzw. Clear Entry).
      * Einmaliges Drücken der Taste löscht die zuvor eingegebenen Ziffern auf dem Bildschirm
@@ -45,10 +51,25 @@ public void pressDigitKey(int digit) {
      * im Ursprungszustand ist.
      */
     public void pressClearKey() {
-        screen = "0";
-        latestOperation = "";
-        latestValue = 0.0;
+        if (!wasClearedOnce) {
+            screen = "0";
+            wasClearedOnce = true;
+        } else {
+            screen = "0";
+            latestOperation = "";
+            latestValue = 0.0;
+            wasClearedOnce = false;
+        }
+
+
     }
+    public double getLatestValue() {
+        return latestValue;
+    }
+    public String getLatestOperation() {
+        return latestOperation;
+    }
+
 
     /**
      * Empfängt den Wert einer gedrückten binären Operationstaste, also eine der vier Operationen
@@ -118,6 +139,11 @@ public void pressNegativeKey() {
      * und das Ergebnis direkt angezeigt.
      */
     public void pressEqualsKey() {
+
+        if (latestOperation.isEmpty()) {
+            return;
+        }
+
         var result = switch(latestOperation) {
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
@@ -129,5 +155,6 @@ public void pressEqualsKey() {
         if(screen.equals("Infinity")) screen = "Error";
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
+        latestValue = 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..2b9e84c 100644
--- a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -87,8 +87,61 @@ void testMultipleDecimalDots() {
 
         assertEquals(expected, actual);
     }
+    //TODO hier weitere Tests erstellen
+
+    @Test
+    @DisplayName("should change sign to postive when pressing negative key twice")
+    void testChangeOfSign() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(6);
+        calc.pressNegativeKey();
+        calc.pressNegativeKey();
+
+        String expected = "16";
+        String actual = calc.readScreen();
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("should do nothing when equals key is pressed without prior operation")
+    void testEqualsKeyWithoutOperation() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(4);
+        calc.pressDigitKey(9);
+        calc.pressEqualsKey();
+
+        String expected = "149";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("should only clear screen on first press and reset memory on second press")
+    void testDoubleClearResetCalculator() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(4);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(2);
+        calc.pressDigitKey(3);
+        calc.pressEqualsKey();
+
+        calc.pressClearKey();
+        assertEquals(27, calc.getLatestValue());
+        assertEquals("+", calc.getLatestOperation());
+
+        calc.pressClearKey();
+        String expected = "0";
+        String actual = calc.readScreen();
+        assertEquals(0, calc.getLatestValue());
+        assertEquals("", calc.getLatestOperation());
+        assertEquals(expected, actual);
+
+    }
 
 
-    //TODO hier weitere Tests erstellen
 }