diff --git a/math.scss b/math.scss
index 5dd2a43..9092e80 100644
--- a/math.scss
+++ b/math.scss
@@ -62,16 +62,26 @@
     $ret: 0;
     $n: 1;
     $dx: .001;
-    
+
     @while $n <= $x {
         $ret: $ret + $dx / $n;
-        
+
         $n: $n + $dx;
     }
-    
+
     @return $ret;
 }
 
-@function sqrt($x) {    
+@function sqrt($x) {
     @return exp(0.5 * ln($x));
 }
+
+@function atan ($x) {
+  $ret: 0;
+
+  @for $n from 0 to 25 {
+    $ret: $ret + power(-1, $n) * power($x, 2 * $n + 1) / (2 * $n + 1);
+  }
+
+  @return $ret;
+}
diff --git a/test.html b/test.html
index ed586aa..59465bf 100644
--- a/test.html
+++ b/test.html
@@ -11,6 +11,7 @@
         <div class="test" id="test-exp">e^x function</div><!-- e^x --><br />
         <div class="test" id="test-ln">ln function</div><!-- ln -->
         <div class="test" id="test-sqrt">Sqrt function</div><!-- sqrt -->
+        <div class="test" id="test-atan">Atan function</div><!-- sqrt -->
     </body>
 
-</html>
\ No newline at end of file
+</html>
diff --git a/test.scss b/test.scss
index 0619b4b..3582ac8 100644
--- a/test.scss
+++ b/test.scss
@@ -41,6 +41,12 @@
 #test-ln {
     @if ln(exp(1)) != 1.001 { background-color:red; };
 }
+
 #test-sqrt {
     @if sqrt(4) != 2 { background-color:red; };
-}
\ No newline at end of file
+}
+
+#test-atan {
+    @if atan(0) != 0 { background-color: red; }
+    //@if atan(1) != 0.79539 { background-color: red; }
+}