function CheckZero(field) {
        if (field.value == 0 || field.value.length == 0) {
            alert ("This field cannot be 0.");
            field.focus(); }
        //else
	    //calculate Re-Payment
    }

    function cmdCalc_Click(form) {
        if (form.txtHowMuch.value == 0 || form.txtHowMuch.value.length == 0) {
            alert ("Please enter your mortgage amount.");
            form.txtHowMuch.focus(); }
        else if (form.oldrate.value == 0 || form.oldrate.value.length == 0) {
            alert ("Please enter your current interest rate.");
            form.oldrate.focus(); }
	    else if (form.newrate.value == 0 || form.newrate.value.length == 0) {
            alert ("Please enter the new interest rate.");
            form.newrate.focus(); }
        else if (form.txtPaymentPeriod.value == 0 || form.txtPaymentPeriod.value.length == 0) {
            alert ("Please enter your mortgage term.");
            form.txtPaymentPeriod.focus(); }
        else
            calculatePayment(form);
    }

    function calculatePayment(form) {
     
      //get values from the input form
		var princ = form.txtHowMuch.value;
		var rate = (form.oldrate.value);
		var newrate = (form.newrate.value);
		var intRate = (form.oldrate.value/100) /12;
		var txtPaymentPeriod = form.txtPaymentPeriod.value
		var newintrate = (form.newrate.value/100) /12;
        var months = form.txtPaymentPeriod.value * 12;
        
		//calculate the repayments on repayment motgage
		var repayment = Math.floor((princ*intRate)/(1-Math.pow(1+intRate,(-1*months)))*100)/100;
		var newrepayment = Math.floor((princ*newintrate)/(1-Math.pow(1+newintrate, (-1*months)))*100)/100;
 	
		//calculate the repayments on an interest only mortgage
		var I = rate / 12;
		var X = 1/(1+I/100);
		var I2 = newrate / 12
		var X2 = 1/(1+I2/100);
		var N = txtPaymentPeriod * 12;
		var L = princ;
		var P1 = 0;
		var P2 = princ;
		//var A1 = (L - P1 * Math.pow(X,N)) * (X - 1)/(Math.pow(X,N+1)-X) - REPAYMENT CALC
		var A1 = round((L - P2 * Math.pow(X,N)) * (X - 1)/(Math.pow(X,N+1)-X),2);
		var A2 = round((L - P2 * Math.pow(X2,N)) * (X2 - 1)/(Math.pow(X2,N+1)-X2),2);
	
		//populate the fields for a repayment mortgage
		form.repaysaving.value = round((repayment-newrepayment),2)
		
		//populate the fields for an interest only mortgage
		form.intsaving.value = round((A1-A2),2)
		}
		
function round(number,X) {
// rounds number to X decimal places, defaults to 2
X = (!X ? 2 : X);
return Math.round(number*Math.pow(10,X))/Math.pow(10,X);
}