The idea is to ask people to self-assess where they fit on a scale from closed book to open book. They do not need to reveal their "privacy reading" but they do need to think about whether or not it is fair to impose their position on others.
In other words, there is no correct reading, but plenty of scope to use the meter as a basis for discussion. For example, suppose you are an open book. Is it fair to make others become open book about their personal data if they prefer to be more of a closed book? On the other hand, if you think you are a closed book, are you prepared to provide information about yourself in order to authenticate your identity and establish trust?