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 84c04f2..ba35578 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -31,7 +31,7 @@ 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 = "";
 
         screen = screen + digit;
     }
@@ -60,8 +60,13 @@ public void pressClearKey() {
      * @param operation "+" für Addition, "-" für Substraktion, "x" für Multiplikation, "/" für Division
      */
     public void pressBinaryOperationKey(String operation)  {
+
+        if (!latestOperation.isEmpty()) {
+            pressEqualsKey();
+        }
         latestValue = Double.parseDouble(screen);
         latestOperation = operation;
+        screen = "0";
     }
 
     /**
@@ -118,6 +123,11 @@ 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);
@@ -130,4 +140,4 @@ 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);
     }
-}
+}
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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 ddff0da..5fba014 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -89,6 +89,64 @@ void testMultipleDecimalDots() {
     }
 
 
-    //TODO hier weitere Tests erstellen
-}
+    @Test
+    @DisplayName("should display result after subtracting two positive multi-digit numbers")
+    void testPositiveSubtraction(){
+
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(3);
+        calc.pressDigitKey(0);
+
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(2);
+        calc.pressDigitKey(0);
+        calc.pressEqualsKey();
+
+        String expected = "10";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+
+    }
+
+    @Test
+    @DisplayName("should display result after subtracting two positive multi-digit numbers")
+    void testEqualsAfterNoNewOperation(){
+
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+
+        calc.pressEqualsKey();
 
+        String expected = "5";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+
+    }
+
+    @Test
+    @DisplayName("should display result after more then 2 Operations")
+    void testMoreThenTwoOperations(){
+
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(5);
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(5);
+        calc.pressDigitKey(0);
+        calc.pressBinaryOperationKey("+");
+        calc.pressDigitKey(5);
+        calc.pressDigitKey(0);
+        calc.pressDigitKey(0);
+        calc.pressEqualsKey();
+
+        String expected = "455";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+
+    }
+}
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