They are all over the place. I have two Motec PLM lambda meters, one on each dyno. I use the NTK sensor on both of mine. I've seen AEM's read the same and i've seen them read as much at 1.5 point higher and lower than the PLM. Basically, i've seen them all over the place. Most people don't have two meters on the same car to begin with, much less 1 high quality meter to compare to. It's much easier to just assume the reading you're getting is right but I don't trust an AEM Uego reading in the least.