compute_top: function compute_top() {

        // to compute from the bottom of the menu, the top offset is incremented by the menu wrap height

        td_affix.top_offset = 0;


        if (jQuery(td_affix.menu_wrap_selector).length && jQuery(td_affix.menu_wrap_selector)) {
            td_affix.top_offset = jQuery(td_affix.menu_wrap_selector).offset().top + jQuery(td_affix.menu_wrap_selector).height();
        }



        //check to see if the menu is at the top of the screen
        if (td_affix.top_offset == (jQuery(td_affix.menu_wrap_selector).height()) + 1) {
            //switch to affix - because the menu is at the top of the page
            //td_affix._affix_on(jQuery(td_affix.menu_selector));
            td_affix.is_top_menu = true;
        } else {
            //check to see the current top offset
            td_affix.is_top_menu = false;

        }
        td_affix.td_events_scroll(jQuery(window).scrollTop());

        //alert(td_affix.top_offset);
        //console.log('computed: ' + td_affix.top_offset);
    },