A simple countdown class

Countdown.as

package com.ee.example.timing
{
    import flash.events.Event;
    import flash.events.EventDispatcher;
    import flash.events.TimerEvent;
    import flash.utils.Timer;

    [Event(type="flash.events.Event", name="countdownComplete")]
    public class Countdown extends EventDispatcher
    {
        public static const COUNTDOWN_COMPLETE:String = "countdownComplete";

        public static const COUNTDOWN_UPDATE:String = "countdownUpdate";

        public static const MINUTES:int = SECONDS * 60;

        public static const SECONDS:int = 1000;

        public var unit:int = SECONDS;

        private var _startValue:int;

        private var isCounting:Boolean;

        private var timer:Timer;

        public function start():void
        {
            timer = new Timer(unit, _startValue);
            timer.addEventListener(TimerEvent.TIMER, onTimer);
            timer.start();
            isCounting = true;
        }

        public function set startValue(value:int):void
        {
            if (isCounting)
            {
                return;
            }

            _startValue = Math.max(value, 1);
            dispatchEvent(new Event(COUNTDOWN_UPDATE));
        }


        public function stop():void
        {
            timer.stop();
            isCounting = false;
            dispatchEvent(new Event(COUNTDOWN_UPDATE));
            removeTimer();
        }

        [Bindable("countdownUpdate")]
        public function get value():int
        {
            if (isCounting)
            {
                return _startValue - timer.currentCount;
            }
            return _startValue;
        }

        private function onTimer(event:TimerEvent):void
        {

            if (value == 0)
            {
                dispatchEvent(new Event(COUNTDOWN_COMPLETE));
                isCounting = false;
                removeTimer();
            }
            dispatchEvent(new Event(COUNTDOWN_UPDATE));
        }

        private function removeTimer():void
        {
            timer.removeEventListener(TimerEvent.TIMER, onTimer);
            timer = null;
        }
    }
}