function zipd($lat1,$lon1,$lat2,$lon2,$unit)
 {
	  $theta = $lon1 - $lon2;
	  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta)); 
	  $dist = acos($dist); 
	  $dist = rad2deg($dist); 
	  $miles = $dist * 60 * 1.1515;
	  $unit = strtoupper($unit);
	
	  if ($unit == "K") {
		return ($miles * 1.609344); 
	  }else if ($unit == "N") {
		return ($miles * 0.8684);
  	  } else {
		return $miles;
	  }
 }