function returnObjById( id )
 {
  if(document.getElementById)
  var returnVar = document.getElementById(id);
  else if (document.all)
  var returnVar = document.all[id];
  else if (document.layers)
  var returnVar = document.layers[id];
  return returnVar;
 }
function calculate() {
	var total = 0;
	for (var i = 1; i < 32; i++) total += Number(numeric(returnObjById("amount_" + i).value, returnObjById("area_" + i).value));
	inv = total;
	inv = inv + "";
	if (inv.indexOf(".") == -1) returnObjById("total").value = inv + ".00";
	else if ((inv.length - inv.indexOf(".")) == 2) returnObjById("total").value = inv + "0";
	else returnObjById("total").value = inv.substring(0, inv.indexOf(".") + 3);
}
function makeNumerical(o) {
	var bag = "0123456789";
	var s = "";
	for (var i = 0; i < o.value.length; i++) if (bag.indexOf(o.value.charAt(i)) != -1) s += o.value.charAt(i);
	o.value = s;
}
function numeric(a, b) {
	v = a * b;
	v = (v * 100) / 100;
	v = v.toString();
	var p = v.indexOf('.');
	if (p == -1) return v + ".00";
	p = v.length - p;
	if (p == 2) return v + "0";
	return v;
}