function checkNumber(input, min, max, msg)
{
    msg = msg + " field has invalid data: " + input.value;

    var str = input.value;
        
    for (var i = 0; i < str.length; i++) {
        var ch = str.substring(i, i + 1)
        if ((ch < "0" || "9" < ch) && ch != '.') {
            alert(msg);
            
            return false;
        }
    }
    var num = parseFloat(str)
    if (num < min || max < num) {
        alert(msg + " not in range [" + min + ".." + max + "]");
        return false;
    }
    input.value = str;
    return true;
}

function computeField(input)
{
    //if (input.value != null && input.value.length != 0)
	//input.value = "" + eval(input.value);
    computeForm(input.form);
}

function computeForm(form)
{
    if ((form.payments.value == null || form.payments.value.length == 0) ||
       // (form.interest.value == null || form.interest.value.length == 0) ||
        (form.deposit.value == null || form.deposit.value.length == 0) ||
        (form.principal.value == null || form.principal.value.length == 0)) {
        return;
    }

    if (!checkNumber(form.deposit, 0, 1000000, "Deposit")) {
		document.getElementById("payment").innerHTML = "";
        //form.payment.value = "Invalid";
        return;
    }
	var dep = form.principal.value / 100 * 30;
	
	if (form.deposit.value < dep){
		alert("You must have a 30% deposit to qualify for this offer.");
		clearForm(form);
		return;
	}
	
	var balance = (form.principal.value - form.deposit.value)
   // var i = form.interest.value;
   // if (i > 1.0) {
    //    i = i / 100.0;
   //     form.interest.value = i;
   // }
   // i /= 12;
    //i = 0;

   // var pow = 1;
   // for (var j = 0; j < form.payments.value; j++)
    //    pow = pow * 1;
    //form.payment.value = (form.principal.value * pow) / (pow - 1)
    var totVal = new ToFmt(balance / form.payments.value);
    //form.payment.value = trim(totVal.fmtF(13,2));
    document.getElementById("payment").innerHTML = trim(totVal.fmtF(13,2));
}

function clearForm(form)
{
   document.getElementById("payment").innerHTML = "";
   //form.payment.value = "";
   // form.interest.value = "";
   form.deposit.value = "";
   // form.principal.value = "";
}