The short answer is get one sensor working, then add another, then use the '-' operator on the results. But there's v. similar posting recently that might be relevant: http://arduino.cc/forum/index.php/topic,123039.0.html
The short answer is get one sensor working, then add another, then use the '-' operator on the results. But there's v. similar posting recently that might be relevant: http://arduino.cc/forum/index.php/topic,123039.0.html