Manuscript Preparation, Copyediting, and Proofreading

Q. I am using the double-numeration system recommended for heavily illustrated books (e.g., 4.1 for chapter 4, illustration 1). My problem is that there are two figures in the book’s preface, which comes before an introduction without illustrations. Numbering such as P.1 or 0.1 could look awkward. How might I number those illustrations?

A. Both of your suggestions are commonly used. Neither is very pretty, but they are practical.