diff --git a/src/main/java/tdd/setup/Calculator.java b/src/main/java/tdd/setup/Calculator.java
index 171f6d6..286e509 100644
--- a/src/main/java/tdd/setup/Calculator.java
+++ b/src/main/java/tdd/setup/Calculator.java
@@ -38,11 +38,14 @@ public void pressDotKey() {
     }
 
     public void pressNegative() {
-        screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+        screen = screen.startsWith("-") ? screen.substring(1) : "-";
+
+
     }
 
     public void pressEquals() {
         var result = switch(latestOperation) {
+            case "%" -> latestValue / 100;
             case "+" -> latestValue + Double.parseDouble(screen);
             case "-" -> latestValue - Double.parseDouble(screen);
             case "x" -> latestValue * Double.parseDouble(screen);
diff --git a/src/test/java/tdd/setup/CalculatorTest.java b/src/test/java/tdd/setup/CalculatorTest.java
index 3bf16e9..eda6eb6 100644
--- a/src/test/java/tdd/setup/CalculatorTest.java
+++ b/src/test/java/tdd/setup/CalculatorTest.java
@@ -6,14 +6,46 @@
 
 @DisplayName("Retro calculator")
 class CalculatorTest {
+
+    private Calculator calc = new Calculator();
     @Test
     @DisplayName("should display result after adding two positive numbers")
     void calculatorCanDoTwoPlusTwo() {
-        Calculator calc = new Calculator();
         calc.pressDigitKey(2);
         calc.pressOperationKey("+");
         calc.pressDigitKey(2);
         calc.pressEquals();
         assertEquals("4", calc.readScreen());
     }
+
+    @Test
+    @DisplayName("should revert screen to 0")
+    void calculatorCanClearScreen(){
+        calc.pressDigitKey(2);
+        calc.pressOperationKey("+");
+        calc.pressDigitKey(2);
+        calc.pressEquals();
+        calc.pressClearKey();
+        assertEquals("0", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("should move decimal point two spaces forward")
+    void calculatorCanDecimalizePercentages(){
+        calc.pressDigitKey(8);
+        calc.pressDigitKey(9);
+        calc.pressDigitKey(8);
+        calc.pressOperationKey("%");
+        assertEquals("8.98", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName ("if the negative key is pressed before the input of a number, the number should turn negative")
+    void calculatorCanDisplayNegativeNumbers () {
+        calc.pressClearKey();
+        calc.pressNegative();
+        calc.pressDigitKey(8);
+        calc.pressDigitKey(8);
+        assertEquals("-88", calc.readScreen());
+    }
 }