function checkForZero(field)
{
    if (field.value == 0 || field.value.length == 0) {
        alert ("This field can't be 0!");
        field.focus(); }
    else
        calculatePayment(field.form);
}

function cmdCalc_Click(form)
{
    if (form.price.value == 0 || form.price.value.length == 0) {
        alert ("The Price field can't be 0!");
        form.price.focus(); }
    else if (form.ir.value == 0 || form.ir.value.length == 0) {
        alert ("The Interest Rate field can't be 0!");
        form.ir.focus(); }
    else if (form.term.value == 0 || form.term.value.length == 0) {
        alert ("The Term field can't be 0!");
        form.term.focus(); }
    else
        calculatePayment(form);
}

function calculatePayment(form)
{
    princ = form.price.value - form.dp.value;
    intRate = (form.ir.value/100) / 12;
    months = form.term.value * 12;
    form.pmt.value = Math.floor((princ*intRate)/(1-Math.pow(1+intRate,(-1*months)))*100)/100;
    form.principle.value = princ;
    form.payments.value = months;
}