function taxan()
   {
//lettura dati
  var i = parseFloat (document.form1.tasso.value);
  var t = parseFloat (document.form1.tempo.value);
  var c = parseInt (document.form1.mod.value);


var uno = i/100;
var due = 1+uno;
var tre = Math.pow(due,t);
var quattro = tre-1;

 if (c==0) var k= ((Math.pow((1+(i/100)),t))-1)*100;
 else k= ((Math.pow((1+(i/100)),(t/c)))-1)*100;
 document.form1.tot.value= Math.round(k*1000000)/1000000;

}