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 calculate() {
		calc(window.document.myForm);
     }

     function calc(form) {
         if (form.PV.value == 0 || form.PV.value.length == 0) {
             alert ("The Price field can't be 0!");
             form.PV.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.YR.value == 0 || form.YR.value.length == 0) {
             alert ("The Term field can't be 0!");
             form.YR.focus(); }
         else
             calculatePayment(form);
     }

     function calculatePayment(form) {
        princ = form.PV.value - form.DN.value;
        intRate = (form.IR.value/100) / 12;
        months = form.YR.value * 12;
        form.MP.value = Math.floor((princ*intRate)/(1-Math.pow(1+intRate,(-1*months)))*100)/100;
   		form.PI.value = princ;
 		form.MT.value = months;
     }