window.onerror = fehlerbehandlung;

  function fehlerbehandlung(nachricht, datei, zeile) {
    alert("Ganz doofer Fehler in Zeile: " + zeile + "\nBrowser meint: " + nachricht);
    return true;
  }
  
  function zoomIn() {
    var quick = Math.round((document.getElementById("das_Blatt").width / document.getElementById("das_Blatt").height) * 100);
    document.getElementById("das_Blatt").width += quick;
    document.getElementById("das_Blatt").height += 100; 
    //alert(document.getElementById("das_Blatt").width + ", " + document.getElementById("das_Blatt").height);
  }
  function zoomOut() {
    var quick = Math.round((document.getElementById("das_Blatt").width / document.getElementById("das_Blatt").height) * 100);
    document.getElementById("das_Blatt").width -= quick;

    document.getElementById("das_Blatt").height -= 100;   
  }
  
  function choose_note() {
  window.location.href = "?src=" + document.getElementById("blattgruppe").value + document.getElementById("blatt").value;
  }

  function plus_note() {
  //quick = parseInt(document.getElementById("blatt").value.substr(1,document.getElementById("blatt").value.length-1), 10);  //alert(quick);
  quick = parseInt(document.getElementById("blatt").value,10);
  quick++;
  if (quick < 10) nullstellen = "00";
  else if (quick < 100) nullstellen = "0";
  else nullstellen = "";
  window.location.href = "?src=" + document.getElementById("blattgruppe").value + nullstellen + quick;
  
  }
  function minus_note() {
  //quick = parseInt(document.getElementById("blatt").value.substr(1,document.getElementById("blatt").value.length-1), 10);  //alert(quick);
  quick = parseInt(document.getElementById("blatt").value,10);
  quick--;
  if (quick < 10) nullstellen = "00";
  else if (quick < 100) nullstellen = "0";
  else nullstellen = "";
  window.location.href = "?src=" + document.getElementById("blattgruppe").value + nullstellen + quick;
  
  }
  function maximieren() {
     document.getElementById("das_fenster").style.width = "970px";
     document.getElementById("das_fenster").style.height = "500px";
     document.getElementById("do_min").style.display = "inline";
     document.getElementById("do_max").style.display = "none";
     
     
     document.getElementById("das_Blatt").height = Math.round(1000 * document.getElementById("das_Blatt").height / document.getElementById("das_Blatt").width);	
     document.getElementById("das_Blatt").width = 1000;
     //alert(document.getElementById("das_Blatt").height);
  }
  function minimieren() {
     document.getElementById("das_fenster").style.width = "800px";
     document.getElementById("das_fenster").style.height = "280px";
     document.getElementById("do_max").style.display = "inline";
     document.getElementById("do_min").style.display = "none";  
  }