diff --git a/maths.hpp b/maths.hpp
index 0fb66b52..48a5edd7 100644
--- a/maths.hpp
+++ b/maths.hpp
@@ -11,7 +11,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
- * Copyright 2010-2014 Danny Robson <danny@nerdcruft.net>
+ * Copyright 2010-2018 Danny Robson <danny@nerdcruft.net>
  */
 
 #ifndef __MATHS_HPP
@@ -81,6 +81,13 @@ namespace util {
     ///////////////////////////////////////////////////////////////////////////
     // Comparisons
     inline bool
+    relatively_equal (float a, float b, float percentage)
+    {
+        return std::abs (1 - b / a ) < percentage;
+    }
+
+    //-------------------------------------------------------------------------
+    inline bool
     almost_equal (float a, float b)
     {
         return ieee_single::almost_equal (a, b);