Hyphens, En Dashes, Em Dashes

Q. My question is regarding page numbers in references. If we have pages ranging from 315 to 317, it is my understanding this should read as 315–7. Now let’s say a journal article is from pages 310 to 319. Does it matter that there is a zero in the beginning page number? Is the proper format 310–9 or 310–19? Someone has informed me that if a zero occurs in the beginning page, we must skip a number back in the ending page. That would mean 310–19, rather than 310–9.

A. There are several ways to condense inclusive numbers. Chicago’s preferred method renders your ranges 315–17 and 310–19 (using en dashes), but one of two alternative methods that we describe would include only the changed part: 315–7 and 310–9. (The other alternative is to include all digits.) This method, though economical, is not as easy to interpret as Chicago’s preferred method. Please see the table in the numbers chapter of CMOS for instructions.