diff --git a/src/main/java/tdd/setup/Calculator.java b/src/main/java/tdd/setup/Calculator.java
index 171f6d6..d9387ef 100644
--- a/src/main/java/tdd/setup/Calculator.java
+++ b/src/main/java/tdd/setup/Calculator.java
@@ -12,10 +12,12 @@ public class Calculator {
     public String readScreen() {
         return screen;
     }
+
     public void pressDigitKey(int digit) {
         if(digit > 9 || digit < 0) throw new IllegalArgumentException();
 
-        if(latestOperation.isEmpty()) {
+        //Bug-Fix No 2
+        if(latestOperation.isEmpty() || !(latestValue == 0.0)) {
             screen = screen + digit;
         } else {
             latestValue = Double.parseDouble(screen);
@@ -37,12 +39,18 @@ public void pressDotKey() {
         if(!screen.endsWith(".")) screen = screen + ".";
     }
 
+    //Bug-Fix No 3
     public void pressNegative() {
-        screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+        if (screen.startsWith("-")) {
+            screen = screen.substring(1);
+        } else{
+            screen = "-" + screen.substring(1);
+        }
     }
 
     public void pressEquals() {
         var result = switch(latestOperation) {
+            case "" -> Double.parseDouble(screen); //Bug-Fix No 1
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
             case "x" -> latestValue * Double.parseDouble(screen);
diff --git a/src/test/java/tdd/setup/CalculatorTest.java b/src/test/java/tdd/setup/CalculatorTest.java
index 3bf16e9..c216ac2 100644
--- a/src/test/java/tdd/setup/CalculatorTest.java
+++ b/src/test/java/tdd/setup/CalculatorTest.java
@@ -16,4 +16,49 @@ void calculatorCanDoTwoPlusTwo() {
         calc.pressEquals();
         assertEquals("4", calc.readScreen());
     }
+
+    @Test
+    @DisplayName("should display result after divide two numbers")
+    void calculatorCanDoFiveDividedFive()
+    {
+        Calculator calc1 = new Calculator();
+        calc1.pressDigitKey(5);
+        calc1.pressOperationKey("/");
+        calc1.pressDigitKey(5);
+        calc1.pressEquals();
+        assertEquals("1", calc1.readScreen());
+    }
+
+    @Test
+    @DisplayName("should display show the same digit after press 'equals'")
+    void calculatorCanDoSixEquals() {
+        Calculator calc2 = new Calculator();
+        calc2.pressDigitKey(6);
+        calc2.pressEquals();
+        assertEquals("6", calc2.readScreen());
+    }
+
+    @Test
+    @DisplayName("should display show the result of multiplying of two digit numbers")
+    void calculatorCanDoMultiplyTwoTWODIGITNumbers() {
+        Calculator calc3 = new Calculator();
+        calc3.pressDigitKey(1);
+        calc3.pressDigitKey(0);
+        calc3.pressOperationKey("x");
+        calc3.pressDigitKey(2);
+        calc3.pressDigitKey(0);
+        calc3.pressEquals();
+        assertEquals("200", calc3.readScreen());
+    }
+    //System.out.println(calc3.readScreen()); -> Debugger für die Kommandozeile
+
+    @Test
+    @DisplayName("should display a negative number")
+    void calculatorCanNegativeANumber() {
+        Calculator calc4 = new Calculator();
+        calc4.pressDigitKey(8);
+        calc4.pressNegative();
+        System.out.println("Was bisher rauskommt: " + calc4.readScreen());
+        assertEquals("-8", calc4.readScreen());
+    }
 }