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 aaef8862..a082b4af 100644
--- a/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/app/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -33,6 +33,10 @@ public void pressDigitKey(int digit) {
 
         if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
 
+        if(latestOperation == "-" && latestValue == 0){
+            digit = digit * -1;
+        }
+
         screen = screen + digit;
     }
 
@@ -62,6 +66,8 @@ public void pressClearKey() {
     public void pressBinaryOperationKey(String operation)  {
         latestValue = Double.parseDouble(screen);
         latestOperation = operation;
+
+
     }
 
     /**
@@ -127,5 +133,8 @@ public void pressEqualsKey() {
         screen = Double.toString(result);
         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("Infinity"))screen = ("Error");
+
+
     }
 }
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 addc5f26..08506574 100644
--- a/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/app/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -40,6 +40,71 @@ void testSquareRoot() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    @DisplayName("should display result of two decimal numbers multiplied")
+    void testMultiplicationOfDecimalNumbers() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(1);
+        calc.pressDotKey();
+        calc.pressDigitKey(5);
+        calc.pressBinaryOperationKey("x");
+        calc.pressDigitKey(6);
+        calc.pressDotKey();
+        calc.pressDigitKey(2);
+        calc.pressEqualsKey();
+
+        String expected = "9.3";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+
+
+    }
+
+    @Test
+    @DisplayName("should display result of division by zero")
+    void testDivisionByZero() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(8);
+        calc.pressBinaryOperationKey("/");
+        calc.pressDigitKey(0);
+        calc.pressEqualsKey();
+
+
+        String expected = "Error";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @DisplayName("should display result of two negative numbers subtracted")
+    void testSubtractionOfNegativeNumbers() {
+        Calculator calc = new Calculator();
+
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(6);
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(7);
+        calc.pressEqualsKey();
+
+
+        String expected = "-13";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+
+
+
+
+
+
+
+
     //TODO hier weitere Tests erstellen
 }