Judging by the credentials of my colleagues on the witness panel, they might have a better understanding of the custody rating scale, as parole officers or former parole officers.
It's my understanding that the custody rating scale is done by the parole officer. The parole officer weighs several different factors. There are many factors. They are each given a point value, whether it's institutional charges or that they have community contacts, or their crime to begin with and the brutality of their crime. All of these things weigh into a score, and that score is going to determine whether you are classified as a minimum, medium or maximum-security offender.