function setDateRange( days_back ) {
		
		var el_date_from		= $('calendar-field-1');
		var el_date_to			= $('calendar-field-2');
		
		if( !el_date_from || !el_date_to )
			return;
		
		// today
		var date_start		= new Date();
		el_date_to.value	= date_start.getDate().toPaddedString(2) + '/' + ( date_start.getMonth()+1 ).toPaddedString(2) + '/' + date_start.getFullYear();
		
		var days_back		= parseInt( days_back ); 
		switch( days_back ) {
		
			// clear
			case -1:
				el_date_from.value		= 'DD/MM/ลลลล';
				el_date_to.value		= 'DD/MM/ลลลล';
				break;
				
			default:
				var date_end		= new Date();
				date_end.setDate( date_end.getDate() - days_back );
				el_date_from.value	= date_end.getDate().toPaddedString(2) + '/' + ( date_end.getMonth()+1 ).toPaddedString(2) + '/' + date_end.getFullYear();
				break;
		}
	}