Efficient scroll function using setInterval

gistfile1.js

$.fn.scrollFoo = function() {
    'use strict'

    var that = this,
        didscroll = false;

    $(window).scroll(function() {
        didscroll = true;
    });

    setInterval(function() {
        if(didscroll) {
            $(that).each(function(index, that) {
                var sT = $(window).scrollTop();
                
                if (sT < 450) {
                    $(that).velocity();
                } else {
                    $(that).velocity();
                }
            });
        }
    }, 500); //.5ms poll speed (250 is very commmon in other libs)
};
$('#baz').scrollFoo();