Adjusted ERA
ERA against the league and park, where 100 is average and higher is better.
What it actually is. Earned run average adjusted for park and league and scaled so 100 is average, with better pitching giving a higher number rather than a lower one.
What a scout reads off it. It flips earned run average the right way round and puts a pitcher next to his own era. Pedro Martinez's 291 in 2000 sits in a league that scored more runs than any since the 1930s, which is why that season reads as the best of the modern age however you measure it.
Where the lines are. 100 is average, 130 is an ace, anything over 200 across a full starter's season has happened only a handful of times.
Batter's Eye: look up anything in baseball