// JavaScript Document
    function catcalc(cal) {
		var date = cal.date;
        var time = date.getTime();
        // use the _other_ field
        var field = document.getElementById("desde");
		if (field == cal.params.inputField) {
			document.desde = time;
			if ((!document.hasta) || (document.hasta <= time))
			{
				time += 86400000;
				var date2 = new Date(time);
				document.getElementById("hasta").value = date2.print("%d/%m/%y");
			}
			
		}else{
			document.hasta = time;
			if ((document.desde) && (document.desde > time))
			{
				time -= 86400000;
				var date2 = new Date(time);
        		field.value = date2.print("%d/%m/%y");	
			}
		}
//        var date = cal.date;
//        var time = date.getTime()
//        // use the _other_ field
//        var field = document.getElementById("desde");
//        if (field == cal.params.inputField) {
//            field = document.getElementById("hasta");
//            time -= Date.WEEK; // substract one week
//        } else {
//            time += Date.WEEK; // add one week
//        }
//        var date2 = new Date(time);
//        field.value = date2.print("%Y-%m-%d %H:%M");
    }
Event.onReady(function(){
    Calendar.setup({
        inputField     :    "desde",   // id of the input field
        ifFormat       :    "%d/%m/%y",       // format of the input field
        showsTime      :    false,
        timeFormat     :    "24",
        onUpdate       :    catcalc
    });
    Calendar.setup({
        inputField     :    "hasta",
        ifFormat       :    "%d/%m/%y",
        showsTime      :    false,
        timeFormat     :    "24",
        onUpdate       :    catcalc
    });
					   });