function calendar_month( _val ) {
 m =parseInt(document.calform.month.value) +_val;
 y =parseInt(document.calform.year.value);

 if (m <= 0) {
	m =12;
	y -=1;
 } else if (m >= 13) {
	m =1;
	y +=1;
 }

 document.calform.month.value =m;
 document.calform.year.value =y;
 document.calform.submit();
}