I always thought that cels with the ' on it means it's the 
correction layer for the cel.  So A2' cel has correction 
lines and some areas filled for the A2 cel.  But I just 
got this cel that looks like your normal cel, but it's 
labled A2'.  But the sketch doesn't have any lines on it.  
It's kind of hard to explain, just take a look at the 
picture.  So what exactly does ' mean anyway?

-ix needs help