function calculate_price() {
  var k = document.forms['form1'];
  var base_p = Math.abs(k.elements['base_price'].value);
  var desc = k.elements['description'].value;
  var model_no = k.elements['model_no'].value;
  
  if ( k.elements['check_castors'].checked ) {
    base_p += Math.abs(k.elements['check_castors'].value);
    model_no += '+1.2m+HDMI+';
  }
  
  for (x = 0; x < k.elements['tick_delivery'].length; x++) {
    if ( k.elements['tick_delivery'][x].checked ) {
      base_p += Math.abs(k.elements['tick_delivery'][x].value);
      if (x == 0) {
        desc += '+Free+Delivery';
      } else if (x==1) {
        desc += '+Express+Delivery';
      } else {
        desc += '+Saturday+Delivery';
      }
    }
  }
  //alert(k.elements['tick_delivery'].checked);return;
  
  var email = 'nochex@standland.co.uk';
  var q = new String('https://secure.nochex.com/?email=' + email);
  q += '&amount=' + Math.round(base_p * 100) / 100;
  q += '&description=' + model_no + desc;
  
  document.location.href=q;
}