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.principal.value == null || form.principal.value.length == 0)) {
        return;
    }

  	var ia = 0.0759; 
	var ib = 0.0759;	
	var ic = 0.0834;	
	var id = 0.0849;	
  	var ie = 0.0785; 
	var iff = 0.0785;	
	var ig = 0.0889;	
	var ih = 0.0949;	

	var pa =48;
	var pb =60; 
	var pc =66; 
	var pd =72; 
	var pe =48;
	var pf =60; 
	var pg =66; 
	var ph =72; 


	ia /= 12;
	var powa = 1;
    for (var ja = 0; ja < pa; ja++)
    powa = powa * (1 + ia);
    var a = (form.principal.value * powa * ia) / (powa - 1)
	form.paymenta.value = "$"+ eval (Math.round (a))


	
	ib /=12;
	var powb = 1;
    for (var jb = 0; jb < pb; jb++)
    powb = powb * (1 + ib);
    var b = (form.principal.value * powb * ib) / (powb - 1)
	form.paymentb.value = "$"+ eval (Math.round (b))



	ic /=12;
	var powc = 1;
    for (var jc = 0; jc < pc; jc++)
    powc = powc * (1 + ic);
   	var c = (form.principal.value * powc * ic) / (powc - 1)
	form.paymentc.value = "$"+ eval (Math.round (c))

	id /=12;
	var powd = 1;
    for (var jd = 0; jd < pd; jd++)
    powd = powd * (1 + id);
   	var d = (form.principal.value * powd * id) / (powd - 1)
	form.paymentd.value = "$"+ eval (Math.round (d)) 

	ie /= 12;
	var powe = 1;
    for (var je = 0; je < pe; je++)
    powe = powe * (1 + ie);
    var e = (form.principal.value * powe * ie) / (powe - 1)
	form.paymente.value = "$"+ eval (Math.round (e))


	
	iff /=12;
	var powf = 1;
    for (var jf = 0; jf < pf; jf++)
    powf = powf * (1 + iff);
    var f = (form.principal.value * powf * iff) / (powf - 1)
	form.paymentf.value = "$"+ eval (Math.round (f))



	ig /=12;
	var powg = 1;
    for (var jg = 0; jg < pg; jg++)
    powg = powg * (1 + ig);
   	var g = (form.principal.value * powg * ig) / (powg - 1)
	form.paymentg.value = "$"+ eval (Math.round (g))

	ih /=12;
	var powh = 1;
    for (var jh = 0; jh < ph; jh++)
    powh = powh * (1 + ih);
   	var h = (form.principal.value * powh * ih) / (powh - 1)
	form.paymenth.value = "$"+ eval (Math.round (h)) 
 

}

function clearForm(form)
{
   
    form.principal.value = ""
}