It says, I know 612 Chinese characters.
I just did a test on NCIKU and based on my scores their estimate is 612. Here are the results:
What do I think about it? They're generous!
I am trying to read texts aimed at beginners who know at least 500 characters and every second or third sentence there crops up an unknown Hanji. No, I am not complaining. I love it. Perhaps I didn't know readers also include some new vocabulary.
Now I know how to say: 明天我跟外星人一起去看電影。(I am going to watch a film with an alien tomorrow.)