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..203788b7 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -14,6 +14,8 @@ public class Calculator {
 
     private String latestOperation = "";
 
+    private boolean isNewInput = false;
+
     /**
      * @return den aktuellen Bildschirminhalt als String
      */
@@ -31,8 +33,10 @@ public String readScreen() {
     public void pressDigitKey(int digit) {
         if(digit > 9 || digit < 0) throw new IllegalArgumentException();
 
-        if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
-
+        if(screen.equals("0") || screen.equals("Error") || isNewInput) {
+            screen = "";
+            isNewInput = false;
+        }
         screen = screen + digit;
     }
 
@@ -46,7 +50,7 @@ public void pressDigitKey(int digit) {
      */
     public void pressClearKey() {
         screen = "0";
-        latestOperation = "";
+        latestOperation = "";   //Die CE Eingabe wird nicht beachtet. Es werden in jedem Fall alle bisher getätigten Eingaben gelöscht.
         latestValue = 0.0;
     }
 
@@ -62,6 +66,7 @@ public void pressClearKey() {
     public void pressBinaryOperationKey(String operation)  {
         latestValue = Double.parseDouble(screen);
         latestOperation = operation;
+        isNewInput = true;
     }
 
     /**
@@ -77,11 +82,12 @@ 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); //1 / 0 ergibt infinity, wird hier nicht behandelt
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
         if(screen.equals("NaN")) screen = "Error";
+        if(screen.equals("Infinity")) screen = "Error";
         if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
 
     }
@@ -105,7 +111,7 @@ public void pressDotKey() {
      * entfernt und der Inhalt fortan als positiv interpretiert.
      */
     public void pressNegativeKey() {
-        screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+        screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;  //so in Ordnung
     }
 
     /**
@@ -122,12 +128,12 @@ public void pressEqualsKey() {
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
             case "x" -> latestValue * Double.parseDouble(screen);
-            case "/" -> latestValue / Double.parseDouble(screen);
+            case "/" -> latestValue / Double.parseDouble(screen);  //Analog zu oben; latestValue / 0 führt zu einem Fehler
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
-        if(screen.equals("Infinity")) screen = "Error";
+        if(screen.equals("Infinity")) screen = "Error";             //In keinem Ergebnis kann "Infinity" im String stehen
         if(screen.endsWith(".0")) screen = screen.substring(0,screen.length()-2);
-        if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
+        if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);  //Die Gesamtlänge der Zahl wird hier auf 10 Stellen Begrenzt. Soll eigentlich mit "e" und der Potenz Arbeiten.
     }
 }
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..eca01171 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -88,7 +88,49 @@ void testMultipleDecimalDots() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    @DisplayName("Ersetzt auf dem Display die 0, wenn eine Zahl zwischen 1 und 9 nachfolgend gedrückt wird")
+    void testPressDigitKey(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(5);
 
+        String expected = "5";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("Anfügen mehrerer gleicher aufeinanderfolgender Zahlen")
+    void testPressDigitKeyWholeNumber(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(3);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(3);
+        calc.pressDigitKey(4);
+
+        String expected = "34";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("1/X wirft bei screen = 0 einen Error")
+    void testDivideOneByZero(){
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("1/x");
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
     //TODO hier weitere Tests erstellen
 }