Probably already said but...

You know you are a GOOD arc welder when you don't have to chip slag at all because it just falls off.

I was at our local Tech school taking my reoccurring structural test for all positions with 3" pipe. I take the test there because there instructors are certified by the state. The day I was there they were conducting a arc welding class with mostly newbies. I was going def from all the chipping hammers. I started welding and after about 15 minutes I noticed about 10 students over my shoulder in amazement. They asked for my best advice... I told them... "Don't whale with you chipping hammers, your instructors listen to how much chipping you do because poor welds tend to hold slag and they can tell how good your welds are by how much pounding you are doing". Let's just say the rest of the day was a little quieter at least.