I have used one of these, http://www3.towerhobbies.com/cgi-bin...&I=LXPX81&P=ML but I don't like to tune with them. If you tune the plane while level for max rpm then your gonna end up too lean and it will die when going straight up. It can be a useful tool to compare props, but I wouldn't actually tune with it. That's just how I feel.