D.J. Racing takes nothing for granted and checks every single rocker arm it installs on an engine. This gauge is pretty cool. You can crank 0.100 into the micrometer and the other end should move 0.170 if you're checking a 1.7 rocker arm. The interesting thing is that the movement isn't totally linear. A rocker arm ratio of 1.7 is really an average of the total movement. And you thought building Corvette engines was easy? If you're serious, you check every single component. Danny does. Maybe that's why his Corvettes win so damn much.