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 ("Please enter a house price");
            form.price.focus(); }
        else if (form.ir.value == 0 || form.ir.value.length == 0) {
            alert ("Please enter an interest rate");
            form.ir.focus(); }
        else if (form.term.value == 0 || form.term.value.length == 0) {
            alert ("Please enter a length of term");
            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;
}