I've had 2 so far, the first was really off and the ground screw wouldn't stay tightened. My second was also funny and reading high and always climbing up in resistance. I played with the ground screw a few days ago and found if I center the washer under the screw and then tighten it good I now have had a rock solid correct (agrees with steam engine) ohms reading for the past week on this coil. If it goes back to misbehaving I will try to solder the ground to the 510 connection. I believe the case ground in this mod is a weak point. But for $95 shipped I don't mind fiddling a bit with it. Otherwise its a really well built mod.
.