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..39722c53 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -1,5 +1,6 @@
 package htw.berlin.prog2.ha1;
 
+
 /**
  * Eine Klasse, die das Verhalten des Online Taschenrechners imitiert, welcher auf
  * https://www.online-calculator.com/ aufgerufen werden kann (ohne die Memory-Funktionen)
@@ -8,6 +9,8 @@
  */
 public class Calculator {
 
+    private boolean used = false;
+
     private String screen = "0";
 
     private double latestValue;
@@ -45,9 +48,14 @@ public void pressDigitKey(int digit) {
      * im Ursprungszustand ist.
      */
     public void pressClearKey() {
-        screen = "0";
-        latestOperation = "";
-        latestValue = 0.0;
+        if(!used){
+            screen = "0";
+            used = true;
+        }
+        else {
+            latestValue = 0.0;
+            latestOperation = "";
+        }
     }
 
     /**
@@ -81,6 +89,7 @@ public void pressUnaryOperationKey(String operation) {
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
+        if(screen.equals("Infinity")) screen = "Error";
         if(screen.equals("NaN")) screen = "Error";
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
 
@@ -106,6 +115,7 @@ public void pressDotKey() {
      */
     public void pressNegativeKey() {
         screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+
     }
 
     /**
@@ -130,4 +140,18 @@ public void pressEqualsKey() {
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
     }
+
+    public static void main(String[] args) {
+        double i = 55;
+        double b = 0;
+
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("1/x");
+
+        System.out.println(calc.readScreen());
+    }
 }
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..b65728ba 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -56,6 +56,23 @@ void testDivisionByZero() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    @DisplayName("should display the result after dividing two positive numbers")
+    void testDivisionPositiveNumbers() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(9);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(3);
+        calc.pressEqualsKey();
+
+        String expected = "3";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+
     @Test
     @DisplayName("should display error when drawing the square root of a negative number")
     void testSquareRootOfNegative() {
@@ -88,7 +105,45 @@ void testMultipleDecimalDots() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    @DisplayName("check press clear key")
+    void testClearKey() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+        calc.pressBinaryOperationKey("+");
+
+        calc.pressClearKey();
+        calc.pressEqualsKey();
+
+        String expected = "5";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+
+
+
+
 
     //TODO hier weitere Tests erstellen
+
+    @Test
+    @DisplayName("check inverse with division by zero")
+    void testPressNegative() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("1/x");
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+
+    }
 }