function moveScroll(){
    var scroll = $(window).scrollTop();
    var anchor_top = $("#top_anchor").offset().top;
    var anchor_bottom = $("#bottom_anchor").offset().top;
    if (scroll>anchor_top && scroll<anchor_bottom) {
    clone_table = $("#timetable-clone");
    if(clone_table.length == 0){
        clone_table = $("#timetable").clone();
        clone_table.attr('id', 'timetable-clone');
        clone_table.css({position:'fixed',
                 'pointer-events': 'none',
                 top:0});
        clone_table.width($("#timetable").width());
        $("#timetable-container").append(clone_table);
        $("#timetable-clone").css({visibility:'hidden'});
        $("#timetable-clone thead").css({visibility:'visible', 'pointer-events':'auto', 'opacity': '0.0'}).animate({opacity: 1.0});
    }
    } else {
    $("#timetable-clone").remove();
    }
}
$(window).scroll(moveScroll);