function umrechnen(clicked) {

	if (document.forms && document.forms['visko_konverter']) {

		var amount = document.forms['visko_konverter'].amount.value;
		var art = document.forms['visko_konverter'].unit_from.value;
		var nkstellen = parseInt(document.forms['visko_konverter'].nkstellen.value);
		var to;
		var amount_int = amount - 0;
		var erg = 0;

		if ( art == 'cP2WT' ) {
			var erg = 0.2156 * (Math.pow( amount, 0.8436));
		}
		else if ( art == 'WT2cP' ) {
			var erg = Math.pow((4.6382*amount),1.1854);
		}
		else
			var erg = 5;
		
		erg = runde( erg, nkstellen);
		document.forms['visko_konverter'].ergebniss.value = erg;
		
	
	}
}

function runde(x, n) {
  if (n < 1 || n > 14) return false;
  var e = Math.pow(10, n);
  var k = (Math.round(x * e) / e).toString();
  if (k.indexOf('.') == -1) k += '.';
  k += e.toString().substring(1);
  return k.substring(0, k.indexOf('.') + n+1);
}