What is the Dewey classification number for "The Cambridge Companion to the recorder" edited by John Mansfield Thomson (ISBN 0-521-35816-7)? According to the publisher it is 788.36 from 788.36 Recorders. At the Cambridge website they list the call number like this:

Dewey number: 788.3/6
Dewey version: 20

Knowing that they are using the revised 780 schedule means I can use their number directly without having to calculate it myself. Although, in this case I did, because working backwards from a known good value helps me to understand the classification process.