diff --git a/src/main/java/htw/berlin/prog2/ha1/Calculator.java b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
index 84c04f2..de10f4b 100644
--- a/src/main/java/htw/berlin/prog2/ha1/Calculator.java
+++ b/src/main/java/htw/berlin/prog2/ha1/Calculator.java
@@ -29,11 +29,13 @@ public String readScreen() {
      * @param digit Die Ziffer, deren Taste gedrückt wurde
      */
     public void pressDigitKey(int digit) {
-        if(digit > 9 || digit < 0) throw new IllegalArgumentException();
+            if(digit > 9 || digit < 0) throw new IllegalArgumentException();
 
-        if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
+            if(screen.equals("0") || latestValue == Double.parseDouble(screen)) screen = "";
+            if (screen.length() < 9) {
+                screen = screen + digit;
+            }
 
-        screen = screen + digit;
     }
 
     /**
@@ -62,8 +64,12 @@ public void pressClearKey() {
     public void pressBinaryOperationKey(String operation)  {
         latestValue = Double.parseDouble(screen);
         latestOperation = operation;
+
     }
 
+
+  
+
     /**
      * Empfängt den Wert einer gedrückten unären Operationstaste, also eine der drei Operationen
      * Quadratwurzel, Prozent, Inversion, welche nur einen Operanden benötigen.
@@ -81,9 +87,8 @@ public void pressUnaryOperationKey(String operation) {
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
-        if(screen.equals("NaN")) screen = "Error";
-        if(screen.contains(".") && screen.length() > 11) screen = screen.substring(0, 10);
-
+        if(screen.equals("NaN")  || screen.equals("Infinity") )  screen = "Error";
+        if(screen.contains(".")  && screen.length() > 11) screen = screen.substring(0, 10);;
     }
 
     /**
diff --git a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
index ddff0da..e0362f0 100644
--- a/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
+++ b/src/test/java/htw/berlin/prog2/ha1/CalculatorTest.java
@@ -90,5 +90,57 @@ void testMultipleDecimalDots() {
 
 
     //TODO hier weitere Tests erstellen
-}
 
+    @Test
+    @DisplayName("should display result after subtracting two positive numbers")
+    void testPositiveSubtraction() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(9);
+        calc.pressBinaryOperationKey("-");
+        calc.pressDigitKey(4);
+        calc.pressEqualsKey();
+
+        String expected = "5";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+    @Test
+    @DisplayName("should limit input number to 9 digits")
+    void testInput() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(9);
+
+
+        String expected = "999999999";
+        String actual = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+   @Test
+    @DisplayName("should display error when calculating inverse of zero")
+    void testInverse0zero() {
+        Calculator calc = new Calculator();
+
+        calc.pressDigitKey(0);
+        calc.pressUnaryOperationKey("1/x");
+
+        String expected = "Error"; // 1/0= Error
+        String actual  = calc.readScreen();
+
+        assertEquals(expected, actual);
+    }
+
+}
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