if (((navigator.appName.charAt(0)=="N") && (navigator.appVersion.charAt(0)>=3))
 || (navigator.appVersion.charAt(0)>=4)) 
 {
 
 if (((navigator.appName.charAt(0)=="N") && (navigator.appVersion.charAt(0)>=3))
 || (navigator.appVersion.charAt(0)>=4)) 
 {
 imgOn = eval(imgName + ".src");
 document [anchor].src = imgOn;
 }
 }
 
 function compute()
{
var pay = checkPayment();
var interest = checkInterest();
var term = checkTerm();
if((pay == 0) || (interest == 0) || (term == 0))
{

}
else 
{
var i = document.ira.interest.value / 100;
var n = document.ira.term.value /1;
var p = document.ira.payment.value / 1;

i = i/12;
n = n*12; 
var a = 1 + i;
var b = Math.pow(a,n);
var c = (b - 1)/i;
var d = c * p;
d = d * 100;
d= Math.floor(d);
d = d / 100;
var total= d;

document.ira.final_value.value= total;
}
}

function checkPayment()
{
if(document.ira.payment.value <= 0)
{
window.alert('You must enter a monthly payment value');
return 0;
}
return 1;
}

function checkInterest()
{
if(document.ira.interest.value <= 0)
{
window.alert('You must enter an interest value greater than 0');
return 0;
}
return 1;
}

function checkTerm()
{
if(document.ira.term.value <= 0)
{
window.alert('You must enter a term longer than 0');
return 0;
}
return 1;
}