Report intevals of percentage of webpage scrolled by user

jquery.reportViewProgress.js

/**
 * Author: Shaunak Vairagare
 * Licence: MIT
 * Plugin Url: https://gist.github.com/shaunakv1/4d187d9f445427ed31814735a575801c
 * 
 * jQuery Plugin to report viewProgress on a element. Usually this will be used on window object, to 
 * detect how much of the page user has seen, and to get a callback each time. 
 *   
 *   Usage Example:
 *   $(window).reportViewProgress({
 *   	reportResolution:10.0,
 *      onProgress: function(pct){
 *     	 console.log(pct + "% page seen");
 *      }
 *   })
 * 
 *   Options:
 *   
 *   reportResolution: If specified, the onProgress callback will only be called after user views in steps the percentage of page specified here.
 *   
 *   onProgress: callback that provides percent of page viewed by user, as the user scrolls.
 **/ 
 
(function ( $ ) {
    $.fn.reportViewProgress = function( options ) {
        var elem = this;
        // This is the easiest way to have default options.
        var settings = $.extend({
            //At what resolution in percentage would you like to know if user has scrolled
            reportResolution: null,
            // callback function to report the page viewed amount. if reportResolution is 
            // not specified onView will report every scroll percent. 
            // If reportResolution is specified than the callback with report progress in steps
            // of reportResolution
            onProgress: null
        }, options );
 
        //At what resolution in percentage would you like to know if user has scrolled
        var reportResolution = 10;//%

        //Tracking Variables
        var lastScrollTop = $(elem).scrollTop();
        var seen = $(elem).height() + lastScrollTop; 
        var seenPct = seen*100.00/$(document).height(); 
        var reported = 0;

        // Start monitoring the scroll and report the exact percnt of page seen
        $(elem).scroll(function(){     
            if( $(elem).scrollTop() > lastScrollTop){      
                 seen = seen + $(elem).scrollTop() - lastScrollTop;
                 lastScrollTop = $(elem).scrollTop();
                 seenPct = Math.round(seen * 100.00 / parseFloat($(document).height()));
                 
                 if(settings.reportResolution) reportScrollEvent(seenPct)
                 else if(settings.onProgress) settings.onProgress(seenPct);
            }

        })

        // function that quantizes the seen percentage to the resolution user has set, and reports once per every resolution crossed
        function reportScrollEvent(seenPct){
            var current = (seenPct - ( seenPct % settings.reportResolution)) / settings.reportResolution;
            if(current > reported){
                reported = current;
                //console.log(reported * settings.reportResolution + "% page seen");  
                if(settings.onProgress) settings.onProgress(reported * settings.reportResolution);
            }
        }
				
        //make an initial report in case page is already scrolled on load
        if(settings.reportResolution) reportScrollEvent(seenPct)
        else if(settings.onProgress) settings.onProgress(seenPct);
        
        //return the dom to enable chaning if needed
        return elem;
    };
}( jQuery ));

Updated working example on jsFiddle