Reading conventional focus charts

Hi All I just had a quick question about the conventional focus paperwork, 

For instants Ch.179 

US Edge +20 ( this means that the Upstage edge of the gobo is at +20 feet correct?

under the picture there is 11R - 2R ( dose this mean that the centre of the Gobo is at 11 feet upstage and 2 feet stage right? 

With Ch. 148 it's 8 feet upstage with the Scallop @ 4 feet stage right, What is a Scallop?

Going to be doing this with some students and what to be sure I have the right answers to their questions 

thanks John