var picNo;	//global variable for web request
	    var picMax;
	    var timTarget;
	    var timPrefix;
	    var timID;
	    var timCnt=0;
	    
	    function Pic_prev(target, filePrefix)   //move to previous image and kill the timer
	    {
		    init(target, filePrefix);
		    if (--picNo<1) picNo = picMax;
		    target.src= filePrefix + picNo+".jpg";
	    }

	    function Pic_next(target, filePrefix)   //move to next image
	    {
		    init(target, filePrefix);
		    if (++picNo>picMax) picNo = 1;
		    target.src= filePrefix + picNo+".jpg";
		    timID = setTimeout("tim_next()",10000);
	    }
	    
        function tim_next() 
        {
            if (!(timTarget== null || timPrefix == null) && (++timCnt < 100))
            {
                Pic_next(timTarget, timPrefix);
            }
        }
        
	    function init(target, filePrefix)
	    {
		    if (picNo==null)    //starting point for display
		    {
			    picNo = 1;
			    picMax = 4;
		    }
		     
		    if (timID != null)  //kill any existing requests
		    {
		        clearTimeout(timID);
		        timID = null;
		    }
		    timTarget = target; //save target and file prefix
		    timPrefix = filePrefix;
	    }