diff --git a/src/main/java/tdd/setup/Calculator.java b/src/main/java/tdd/setup/Calculator.java
index 171f6d6..480f4e1 100644
--- a/src/main/java/tdd/setup/Calculator.java
+++ b/src/main/java/tdd/setup/Calculator.java
@@ -1,10 +1,12 @@
 package tdd.setup;
 
+
 // behaviour inspired by https://www.online-calculator.com/
 public class Calculator {
 
     private String screen = "0";
 
+
     private double latestValue;
 
     private String latestOperation = "";
@@ -18,8 +20,12 @@ public void pressDigitKey(int digit) {
         if(latestOperation.isEmpty()) {
             screen = screen + digit;
         } else {
-            latestValue = Double.parseDouble(screen);
-            screen = Integer.toString(digit);
+             if (latestValue == 0) {
+                 latestValue = Double.parseDouble(screen);
+                 screen = "0";
+             }
+           screen = screen + digit;
+
         }
     }
 
@@ -34,11 +40,12 @@ public void pressOperationKey(String operation)  {
     }
 
     public void pressDotKey() {
-        if(!screen.endsWith(".")) screen = screen + ".";
+        if(!screen.contains(".")) screen = screen + ".";
     }
 
     public void pressNegative() {
         screen = screen.startsWith("-") ? screen.substring(1) : "-" + screen;
+
     }
 
     public void pressEquals() {
@@ -47,6 +54,8 @@ public void pressEquals() {
             case "-" -> latestValue - Double.parseDouble(screen);
             case "x" -> latestValue * Double.parseDouble(screen);
             case "/" -> latestValue / Double.parseDouble(screen);
+            case "" -> latestValue = Double.parseDouble(screen);
+            //case "" -> latestValue  Double.parseDouble(screen);
             default -> throw new IllegalArgumentException();
         };
         screen = Double.toString(result);
diff --git a/src/main/main.iml b/src/main/main.iml
new file mode 100644
index 0000000..2185ddd
--- /dev/null
+++ b/src/main/main.iml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/java" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/src/test/java/tdd/setup/CalculatorTest.java b/src/test/java/tdd/setup/CalculatorTest.java
index 3bf16e9..36edc6f 100644
--- a/src/test/java/tdd/setup/CalculatorTest.java
+++ b/src/test/java/tdd/setup/CalculatorTest.java
@@ -16,4 +16,72 @@ void calculatorCanDoTwoPlusTwo() {
         calc.pressEquals();
         assertEquals("4", calc.readScreen());
     }
-}
+
+    @Test
+    @DisplayName("mein test1")
+    void calculatorCanDoTwoMinusTwo() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(2);
+        calc.pressOperationKey("-");
+        calc.pressDigitKey(2);
+        calc.pressEquals();
+        assertEquals("0", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("mein test2")
+    void calculatorCanDoEightyPlusTwenty() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(8);
+        calc.pressDigitKey(0);
+        calc.pressOperationKey("+");
+        calc.pressDigitKey(2);
+        calc.pressDigitKey(0);
+        calc.pressEquals();
+        assertEquals("100", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("mein test3")
+    void calculatorCanDoJustTwo() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(2);
+        calc.pressEquals();
+        assertEquals("2", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("mein test4")
+    void calculatorCanDoClear() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(2);
+        calc.pressOperationKey("-");
+        calc.pressDigitKey(3);
+        calc.pressClearKey();
+        assertEquals("0", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("mein test5")
+    void calculatorCanDoNegative() {
+    Calculator calc = new Calculator();
+    calc.pressNegative();
+    calc.pressDigitKey(2);
+    calc.pressEquals();
+    assertEquals("-2", calc.readScreen());
+    }
+
+    @Test
+    @DisplayName("mein test6")
+    void calculatorCanDot() {
+        Calculator calc = new Calculator();
+        calc.pressDigitKey(0);
+        calc.pressDotKey();
+        calc.pressDigitKey(2);
+        calc.pressDotKey();
+        calc.pressEquals();
+        assertEquals("0.2", calc.readScreen());
+    }
+
+    }
+
diff --git a/src/test/test.iml b/src/test/test.iml
new file mode 100644
index 0000000..9077291
--- /dev/null
+++ b/src/test/test.iml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/java" isTestSource="true" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file