// custom easing called "custom"
$.easing.custom = function (x, t, b, c, d) {
	var src = 1.70158; 
	if ((t/=d/2) < 1) return c/2*(t*t*(((src*=(1.525))+1)*t - src)) + b;
	return c/2*((t-=2)*t*(((src*=(1.525))+1)*t + src) + 2) + b;}
// use the custom easing
$("div.scrollable").scrollable({easing: 'custom', speed: 700});