// duration  script december 2007
	
  var amount; 
  var rate;
  var number_years;
  var interest_rate;
  var interval = new Array();
 
  function calculate(form) {
  amount = form.amount.value;
  rate = form.rate.value;
  future_value = form.future_value.value;
  interest_rate = rate/100; 
  if (form.interval[0].checked == true) 
  {
   number_years = Math.log(future_value/amount)/Math.log(interest_rate + 1);
  }
  if (form.interval[1].checked == true)
  {
   number_years = Math.log((future_value*interest_rate/amount) + 1)/Math.log(interest_rate + 1);
  }
  
  number_years = Math.round(100*number_years)/100;
  form.number_years.value = number_years; 
  }
 
	// Copyright ©Richard A. Howard 2003-2007