Trouble getting the MooTools periodical function working, now working

Periodical Problems

// I am getting the error:
// 'this.clock = this.iterateClock(current, future).periodical(1000, this); is undefined'
// After it display the days left once, it throws the error
//
// This is now the working version

var Main = new Class({

Implements : [Options],
options : {
     release_date : '1 January, 2010',
},
initialize : function(options) {
    this.setOptions(options);
    this.startClock();
},
startClock : function(){
	this.clock = this.iterateClock.periodical(1000, this);
},

iterateClock : function(current, future){
        var current = $time();
	var future = new Date(this.options.release_date);
	future = future.getTime();
	var difference = future - current;
		
	var days = Math.floor((difference / (60 * 60 * 24)) / 1000);
	console.log(days);
},

});