By asking servers how satisfied the customers seem. This is because the servers may be untruthful, or the customer may be very passive.
In the library of congress system of classifying books, books are each given a classification "number" that starts with 1-3 letters. Those letters give you a general idea of topic.
<span>P is the letter for literature so I'm sure that The Complete Works of Mark Twain is under P</span>
