diff --git a/src/main/java/tdd/setup/Calculator.java b/src/main/java/tdd/setup/Calculator.java
index 171f6d6..1bebc53 100644
--- a/src/main/java/tdd/setup/Calculator.java
+++ b/src/main/java/tdd/setup/Calculator.java
@@ -3,7 +3,7 @@
 // behaviour inspired by https://www.online-calculator.com/
 public class Calculator {
 
-    private String screen = "0";
+    private String screen = "";
 
     private double latestValue;
 
@@ -16,7 +16,10 @@ public void pressDigitKey(int digit) {
         if(digit > 9 || digit < 0) throw new IllegalArgumentException();
 
         if(latestOperation.isEmpty()) {
-            screen = screen + digit;
+            if (screen == "0")
+                screen = Integer.toString(digit);
+            else screen = screen + digit;
+
         } else {
             latestValue = Double.parseDouble(screen);
             screen = Integer.toString(digit);
diff --git a/src/test/java/tdd/setup/CalculatorTest.java b/src/test/java/tdd/setup/CalculatorTest.java
index 3bf16e9..d0c6359 100644
--- a/src/test/java/tdd/setup/CalculatorTest.java
+++ b/src/test/java/tdd/setup/CalculatorTest.java
@@ -16,4 +16,38 @@ void calculatorCanDoTwoPlusTwo() {
         calc.pressEquals();
         assertEquals("4", calc.readScreen());
     }
+
+    @Test
+    @DisplayName("should display result 0 after pressing the clear key")
+    void calculatorCanDoClear() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(2);
+        calc.pressOperationKey("x");
+        calc.pressDigitKey(5);
+        calc.pressEquals();
+        calc.pressClearKey();
+        assertEquals("0", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("should display result after pressing a dezimal number")
+    void calculatorCanDoDotKey() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(0);
+        calc.pressDotKey();
+        calc.pressDigitKey(1);
+        assertEquals("0.1", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("should display result after pressing a negative number")
+    void calculatorCanDoNegative() {
+        Calculator calc = new Calculator();
+        calc.pressNegative();
+        calc.pressDigitKey(5);
+        assertEquals("-5", calc.readScreen());
+    }
+
+
+
 }