Detectives with a zero in their classification have earned the respect of their peers. They're
called things like Zeroes, or Zero Class. If Rank 0 detectives keep working their way up, they
can get a 0 for their middle number too, which indicates proficiency in all specializations. They're
called Double-Zero Class detectives, and their number tells you right from the get-go that they're
at the very top of their field. It's the so-called Great Detective class. If they go even further, they
can get a 0 for their first number that shows proficiency in all of those categories, and join the
ranks of the legendary Triple-Zero Class. I've heard that in the fifteen or so years of Detective
Library history, only four detectives have ever earned the number 000.