function overlay(element) {
	el = document.getElementById(element);
	el.style.visibility = (el.style.visibility == "visible") ? "hidden" : "visible";
}

function calcular() {
  document.formulario.cuota.value=""
  if ((document.formulario.importe.value!="")&&(document.formulario.duracion.value!="")&&(document.formulario.interes.value!="")){
    n=document.formulario.duracion.value
        c=document.formulario.importe.value
        i=document.formulario.interes.value
        if (navigator.appName=='Netscape') {
          tmp=new Array('12','4','2','1')
          p=parseFloat(12)
        } else {
          p=parseFloat(12)
        }
        if (i!=0){
          c1=i/(100*p)
          c2=n*p
          c3=Math.pow(1+c1,c2)
          c4=c3/(c3-1)
          a=c*c1*c4
        } else{
          a= c/(p*n)
        }
        document.formulario.cuota.value=Math.round(a)
  }
  return false;
}