diff --git a/src/main/java/Main.java b/src/main/java/Main.java
new file mode 100644
index 0000000..593578b
--- /dev/null
+++ b/src/main/java/Main.java
@@ -0,0 +1,12 @@
+import tdd.setup.Calculator;
+
+public class Main {
+    public static void main(String[] args) {
+        Calculator calculator = new Calculator(); // cmd+option und v
+        calculator.pressDigitKey(3);
+        calculator.pressOperationKey("+");
+        calculator.pressDigitKey(5);
+        calculator.pressEquals();
+        System.out.println(calculator.readScreen());
+    }
+}
diff --git a/src/main/java/tdd/setup/Calculator.java b/src/main/java/tdd/setup/Calculator.java
index 171f6d6..9a3c068 100644
--- a/src/main/java/tdd/setup/Calculator.java
+++ b/src/main/java/tdd/setup/Calculator.java
@@ -17,10 +17,13 @@ public void pressDigitKey(int digit) {
 
         if(latestOperation.isEmpty()) {
             screen = screen + digit;
-        } else {
+        } else if (latestValue == 0.0){
             latestValue = Double.parseDouble(screen);
             screen = Integer.toString(digit);
         }
+        else{
+            screen = screen + digit;
+        }
     }
 
     public void pressClearKey() {
@@ -30,7 +33,14 @@ public void pressClearKey() {
     }
 
     public void pressOperationKey(String operation)  {
-        latestOperation = operation;
+        if (operation != "%") {
+            latestOperation = operation;
+        }
+        else {
+            var result = Double.parseDouble(screen) / 100.0;
+            screen = Double.toString(result);
+            if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
+        }
     }
 
     public void pressDotKey() {
@@ -51,5 +61,7 @@ public void pressEquals() {
         };
         screen = Double.toString(result);
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
+        if(screen.contains(".0E-")) screen = screen.replace(".0E","e");
+        if(screen.contains(".0E")) screen = screen.replace(".0E","e+");
     }
 }
diff --git a/src/test/java/tdd/setup/CalculatorTest.java b/src/test/java/tdd/setup/CalculatorTest.java
index 3bf16e9..4431667 100644
--- a/src/test/java/tdd/setup/CalculatorTest.java
+++ b/src/test/java/tdd/setup/CalculatorTest.java
@@ -16,4 +16,64 @@ void calculatorCanDoTwoPlusTwo() {
         calc.pressEquals();
         assertEquals("4", calc.readScreen());
     }
+    @Test
+    @DisplayName("should display zero after adding")
+    void calculatorCanDoTwoPlusTwoNewWithClearFunction() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(2);
+        calc.pressOperationKey("+");
+        calc.pressDigitKey(2);
+        calc.pressEquals();
+        calc.pressClearKey();
+        assertEquals("0", calc.readScreen());
+    }
+    @Test
+    @DisplayName("should display result of percentage")
+    void calculatorCanDoPercentageOperationKey() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(8);
+        calc.pressOperationKey("%");
+        assertEquals("0.08", calc.readScreen());
+    }
+    @Test
+    @DisplayName("should display big number")
+    void calculatorCanDoCalculateBigNumber() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressOperationKey("x");
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressEquals();
+        assertEquals("1e+12", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("should display small number")
+    void calculatorCanDoCalculateSmallNumber() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(1);
+        calc.pressOperationKey("/");
+        calc.pressDigitKey(1);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressEquals();
+        assertEquals("1e-7", calc.readScreen());
+    }
 }
+// andere Fälle testen
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