The closing code tag must be "</code>" and because you read -- at least in part - the instructions on how to format a question, you do get some (IMHO) useful advice:
in reply to Hints on hoq to create this graph?
Non-specific questions that make no effort to show that you've actually worked at coming up with an answer -- even if that work has failed -- are apt to get only generic answers... like:
- perldoc perldoc
- Learning Perl (O'Reilly - pretty much any edition > 2)
- ...etc ...etc ...etc.