Added comments

parallax.js

@@ -9,28 +9,37 @@ var Parallax = {
         });
         console.log("Parallax Initialised.");
         if (createEvents) {this.createEvents();}
+        //Calculate the initial positions of the images.
         this.calculate();
     },
     calculate: function() {
+        // Get the window dimentions.
         window_top = $(window).scrollTop();
         window_bottom = window_top + $(window).height();
+
         $(this.ident).each(function(){
+            // If the element isn't on the screen, or wasn't initialised, ignore it.
             if (!is_on_screen(this) || !$(this).attr('parallax-offset')) { return; }
             element = $(this);
+            //Calculate the center position of the image
             center_pos = (element.offset().top - $(window).scrollTop()) + (element.height() / 2);
+            // Calculate the position of the center point, relative to the center.
             perc = -(0.5 - ((window_top - center_pos) / window_bottom));
-
+            // Calculate the position of the center of the image from the percentage through the screen.
             pos = Math.round((perc * element.attr('parallax-offset')) * 100) / 100;
+            // Apply the calculated value.
             element.css('background-position',"0px " + pos + "px");
         });
     },
     createEvents: function() {
+        // Create scroll and resize events for Parallax
         $(window).scroll(function() { Parallax.calculate(); });
         $(window).resize(function() { Parallax.initialise(false); })
     },
-    ident: '.parallax'
+    ident: '.parallax' //The identifier for Parallax elements
 }
 
+// Check if the element is on the screen, not necessarily all of it.
 function is_on_screen(elm) {
     var vpH = $(window).height(),
         st = $(window).scrollTop(),