/**
 * Calculate artist fee.
 */
function calculateFee() {
  // Check for errors.
  if(document.getElementById("plz").value.length!=5) {
    alert("Bitte eine gültige Postleitzahl eingeben.");
    document.getElementById("plz").focus();
    return;
  }

  var flags = "";
  if(document.getElementById("backline").checked)
    flags += "B";
  if(document.getElementById("sleep").checked)
    flags += "S";

  var xmlHttp = new XMLHttpRequest();
  xmlHttp.open("GET","gage.php?options="+flags+"&plz="+document.getElementById("plz").value+"&gage="+document.getElementById("gage").value,true);
  xmlHttp.onreadystatechange = function() {
    if(xmlHttp.readyState == 4) {
      document.getElementById("total").innerHTML = xmlHttp.responseText;
    }
  }
  xmlHttp.send(null);
}