exposure calc

<SCRIPT LANGUAGE="JavaScript">
function tt (form){
x = Math.pow(form.aperture.value,2);
y = Math.pow(2,form.EV.value);
iso = (document.form.iso.options[document.form.iso.selectedIndex].value);
if (form.shutter.value <=1)
{
form.shutter.value = "1/" + Math.round ((1/(x/y))*(iso)*1000)/1024 + " th sec";
console.log(x/y);
}
else {form.shutter.value = Math.round (x/y*10)/10*(iso) + " sec";
console.log(x/y);
}
}
</script>