Почему при скроллинге срабатывает событие resize?

window.onresize = resize;
if ( (new Date()).getDay() - 1 < 0) window.numberDayBlock = 0; else window.numberDayBlock = ((new Date()).getDay() - 1);

function resize() {

    if ($(window).width() > 550)
    {
        $('.days_td').css('overflow-x', 'scroll');
        $('.hr_between_days').removeAttr('style');
        $('.left_arrow').hide();
        $('.right_arrow').hide();
        if (!$('.fio_student_name').is(':visible'))
        {
            $('.fio_student_name').show();
        }
        $('.fio_td').width(200);
        $('.table_day').width("100%");
        var calcWidth = $('.section_page').width() - 200;
        $('.days_td').width(Math.floor(calcWidth));
    }else
    {
        $('.days_td').css('overflow-x', 'hidden');
        $('.hr_between_days').css('float', 'left');
        $('.hr_between_days').css('display', 'none');
        $('.left_arrow').show();
        $('.right_arrow').show();

        if ($_GET()['week'])
        {
            numberDayBlock = 0;
        }

        $('.hr_between_days:eq(' + numberDayBlock + ')').fadeIn().css('display','block');
        $('.hr_between_days:eq(' + (numberDayBlock + 1) + ')').fadeIn().css('display','block');

        if ($('.fio_student_name').css('display') != 'block')
        {
            $('.fio_student_name').hide();
        }

        if ($(window).width() > 420)
        {
            $('.table_day').width( (($('.section_page').width() - 64)) / 2);
        }else
        {
            $('.left_arrow').show();
            $('.right_arrow').show();
            $('.table_day').width(($('.section_page').width() - 65));
        }

        $('.fio_td').width(60);
        var calcWidth = $('.section_page').width() - 60;
        $('.days_td').width(Math.floor(calcWidth));
    }
};

$(document).ready(function(){

        $('.wrapper_wait_load_table').hide();
	if ($("form").is("#data_collection"))
	{
                resize();
		$('#data_collection').show();
		$('.pre_schedule_table').show();
	}
});