Cacher is the code snippet organizer for pro developers

$(window).scroll(function() {
    var window_width = $(window).width(),
        window_scrollleft = $(window).scrollLeft(),
        content_width = $("#content").width(),
        bottomfadebar_width = $("#bottomfadebar").width(),

        content_path = content_width - window_width,
        bottomfadebar_path = window_width - bottomfadebar_width,
        bottomfadebar_left = 0;

//  Equations:
//  content_pos = window_scrollleft / content_path;
//  bottomfadebar_pos = bottomfadebar_left / bottomfadebar_path;
//  content_pos = bottomfadebar_pos;

    bottomfadebar_left = window_scrollleft / content_path * bottomfadebar_path;

    $("#bottomfadebar").css("left", bottomfadebar_left + "px");
});