var lastCalc = 0; 
function pvifa(n, i) 
{ 
    return (1 - (1 / Math.pow(1 + i, n)) ) / i; 
} 
 
function calcpay(form) 
{ 
  var o = parseFloat(form.amt.value); 
  var i = parseFloat(form.rate.value) / 1200; 
  var n = parseInt(form.term.value); 
  form.payment.value = Math.floor( o / pvifa(n,i) *100)/100 ; 
  lastCalc = 0; 
  return 0; 
} 

function calcamt(form) 
{ 
  var pmt = parseFloat(form.payment.value); 
  var i = parseFloat(form.rate.value) / 1200; 
  var n = parseInt(form.term.value); 
  form.amt.value = Math.floor( pmt * pvifa(n,i) *100)/100 ; 
  lastCalc = 0; 
  return 0; 
} 
 
function calcOnBlur(form) 
{ 
  return calcpay(form); 
}