How to slow the scrolling of an HTML element to create a simple parallax effect using jQuery.

parallax.js

jQuery( document ).ready( function( $ ) {
	
	var scrollable = $('#branding .navbar-inner');
	var difference = 5;
	
	if ( scrollable.length ) {
		
		var a = document.body;
		var e = document.documentElement;
		
		$( window ).unbind( 'scroll' ).scroll( function () {
			scrollable.css( 'background-position', '0px ' + -( Math.max( e.scrollTop, a.scrollTop ) / difference ) + 'px' );
		} );
		
	}
	
} );