diff --git a/examples/runner.js b/examples/runner.js
index 9355955..3c1dc69 100644
--- a/examples/runner.js
+++ b/examples/runner.js
@@ -50,4 +50,16 @@ test('Point#add()', function(){
   point.should.respondTo('add');
 });
 
+test('Math#sin()', function(){
+  Math.sin(12).should.be.approximately(-0.5365, 1e-3);
+});
+
+test('Math#cos()', function(){
+  Math.cos(0).should.not.be.approximately(10, 1e-3);
+});
+
+test('Math#log()', function(){
+  Math.log(10).should.be.approximately(10, 1e-3);
+});
+
 console.log();
\ No newline at end of file
diff --git a/lib/should.js b/lib/should.js
index f603a35..fa7a4f0 100644
--- a/lib/should.js
+++ b/lib/should.js
@@ -321,6 +321,19 @@ Assertion.prototype = {
     return this;
   },
 
+  /**
+   * Assert within value +- delta (inclusive).
+   *
+   * @param {Number} value
+   * @param {Number} delta
+   * @param {String} description
+   * @api public
+   */
+
+  approximately: function(value, delta, description) {
+    return this.within(value - delta, value + delta, description);
+  },
+
   /**
    * Assert typeof.
    *