diff --git a/.gitignore b/.gitignore
index b0cbf6e..85e6efb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 # Mac OS System
 .DS_Store*
 ._*
+/bin/
diff --git a/src/simplejavacalculator/Calculator.java b/src/simplejavacalculator/Calculator.java
index 18ad91c..b2c1f89 100644
--- a/src/simplejavacalculator/Calculator.java
+++ b/src/simplejavacalculator/Calculator.java
@@ -23,7 +23,7 @@ public enum BiOperatorModes {
     }
 
     public enum MonoOperatorModes {
-        square, squareRoot, oneDividedBy, cos, sin, tan ,log , rate, abs
+        square, squareRoot, oneDividedBy, cos, sin, tan ,inverseTan, log , rate, abs
     }
 
     private Double num1, num2;
@@ -109,6 +109,10 @@ public Double calculateMono(MonoOperatorModes newMode, Double num) {
 
             return Math.tan(Math.toRadians(num));
         }
+        
+        if (newMode == MonoOperatorModes.inverseTan) {
+        	return Math.toDegrees(Math.atan(num));
+        }
         if (newMode == MonoOperatorModes.log) {
             return log10(num);
         }
diff --git a/src/simplejavacalculator/UI.java b/src/simplejavacalculator/UI.java
index 8e9cc4a..b3b501d 100644
--- a/src/simplejavacalculator/UI.java
+++ b/src/simplejavacalculator/UI.java
@@ -51,7 +51,7 @@ public class UI implements ActionListener {
    private final JTextArea text;
    private final JButton but[], butAdd, butMinus, butMultiply, butDivide,
       butEqual, butCancel, butSquareRoot, butSquare, butOneDividedBy,
-      butCos, butSin, butTan, butxpowerofy, butlog, butrate, butabs, butBinary;
+      butCos, butSin, butTan, butInverseTan, butxpowerofy, butlog, butrate, butabs, butBinary;
    private final Calculator calc;
    
    private final String[] buttonValue = {"0", "1", "2", "3", "4", "5", "6",
@@ -99,7 +99,8 @@ public UI() throws IOException {
       butOneDividedBy = new JButton("1/x");      
       butCos = new JButton("Cos");      
       butSin = new JButton("Sin");      
-      butTan = new JButton("Tan");      
+      butTan = new JButton("Tan");
+      butInverseTan = new JButton("Tan^-1");
       butxpowerofy = new JButton("x^y");      
       butlog = new JButton("log10(x)");      
       butrate = new JButton("x%");      
@@ -135,6 +136,7 @@ public void init() {
       butCos.setFont(font);
       butSin.setFont(font);
       butTan.setFont(font);
+      butInverseTan.setFont(font);
       butxpowerofy.setFont(font);
       butlog.setFont(font);
       butrate.setFont(font);
@@ -184,6 +186,7 @@ public void init() {
       panelSub7.add(butCos);
       panelSub7.add(butSin);
       panelSub7.add(butTan);
+      panelSub7.add(butInverseTan);
       panel.add(panelSub7);
       
       panelSub8.add(butlog);
@@ -192,6 +195,7 @@ public void init() {
       panelSub8.add(butBinary);
       panel.add(panelSub8);
       
+      
       for (int i = 0; i < 10; i++) {
          but[i].addActionListener(this);
       }      
@@ -205,6 +209,7 @@ public void init() {
       butCos.addActionListener(this);
       butSin.addActionListener(this);
       butTan.addActionListener(this);
+      butInverseTan.addActionListener(this);
       butxpowerofy.addActionListener(this);
       butlog.addActionListener(this);
       butrate.addActionListener(this);
@@ -279,6 +284,9 @@ public void actionPerformed(ActionEvent e) {
 
          if (source == butTan)
             writer(calc.calculateMono(Calculator.MonoOperatorModes.tan, reader()));
+         
+         if (source == butInverseTan)
+             writer(calc.calculateMono(Calculator.MonoOperatorModes.inverseTan, reader()));
 
          if (source == butlog)
             writer(calc.calculateMono(Calculator.MonoOperatorModes.log, reader()));
diff --git a/src/simplejavacalculatorTest/CalculatorTest.java b/src/simplejavacalculatorTest/CalculatorTest.java
index 1ea20f7..391bf65 100755
--- a/src/simplejavacalculatorTest/CalculatorTest.java
+++ b/src/simplejavacalculatorTest/CalculatorTest.java
@@ -97,6 +97,12 @@ void CalculateMonoTanTest() {
 		Assertions.assertEquals(1.0, calculator.calculateMono(Calculator.MonoOperatorModes.tan, java.lang.Math.PI / 4), 0.0000000001);
 	}
 	
+	@Test
+	void CalculateMonoInverseTanTest() {
+		Calculator calculator = new Calculator();
+		Assertions.assertEquals(45.0, calculator.calculateMono(Calculator.MonoOperatorModes.inverseTan, 1.0), 0.0000000001);
+	}
+	
 	@Test
 	void CalculateMonoLogTest() {
 		Calculator calculator = new Calculator();