function getStyleObject(objectId) {

  if(document.getElementById && document.getElementById(objectId)) {
	return document.getElementById(objectId).style;
   }
   else if (document.all && document.all(objectId)) {  
	return document.all(objectId).style;
   } 
   else if (document.layers && document.layers[objectId]) { 
	return document.layers[objectId];
   } else {
	return false;
   }
}

function changeObjectVisibility(objectId, newVisibility) {

    var styleObject = getStyleObject(objectId);

    if (styleObject) {
	styleObject.visibility = newVisibility;
	return true;
    } else {
	return false;
    }
}

function getChange(chosen) {

var myindex  = chosen.selectedIndex
var SelValue = chosen.options[myindex].value

if (SelValue == "00") {

  changeObjectVisibility("maxCO", "hidden");
  changeObjectVisibility("maxHS", "hidden");
  changeObjectVisibility("maxO", "hidden");
 
}

if (SelValue == "CO" || SelValue == "HS" || SelValue == "AP") {
 
  changeObjectVisibility("maxCO", "visible");
  changeObjectVisibility("maxHS", "visible");
  changeObjectVisibility("maxO", "hidden");
}
if (SelValue == "O2") {
 
  changeObjectVisibility("maxO", "visible");
  changeObjectVisibility("maxCO", "hidden");
  changeObjectVisibility("maxHS", "hidden");
 
}
if (SelValue == "ME") {

  changeObjectVisibility("maxCO", "visible");
  changeObjectVisibility("maxO", "hidden");
  changeObjectVisibility("maxHS", "hidden");
  
} 
}