The number line, or printer’s key, often seen on the copyright page of books is simply a method of record-keeping that helps identify the book’s printing and, for some, year of printing a specific book, which may or may not be different than the original copyright date listed elsewhere on the page.

Common examples of these number lines include:

1 2 3 4 5 6 7 8 9 10

or

2 3 4 5 6 93 92 91 90

or

3 4 5 6 7 8 9 10 MPC 19 18 17 16

or even

1 3 5 7 9 10 8 6 4 2.

While different publishers use different conventions for these number lines, generally speaking, the smallest number in the line indicates a books printing. So if 1 2 3 4 5 6 7 8 9 10 is at the bottom of the page, it is a first printing; if the number one has been removed, so the number line is 2 3 4 5 6 7 8 9 10, it is a second printing; and if it’s 3 4 5 6 7 8 9 10, it is a third printing, etc.

The reason they remove a number each time instead of, say, just changing one number has to do with the way publishers have historically printed books.  For instance, in offset printing (see our article which covers offset printing- How Do They Get the Ms on M&Ms?), you can relatively easily remove something from the printing plate, but adding a number would require creating a whole new plate.

In any event, sometimes number lines are accompanied by the words First edition but that does not necessarily mean it is the first printing; for example, this would indicate a third printing of a first edition:

First edition

3 4 5 6 7 8 9 10

There may be many printings of an edition, the latter of which may be defined as a single “setting-up of type without substantial change.” So, if the author doesn’t change the text of the book (like text books authors frequently do), and the pages all stay the same, then if the publisher simply makes another round of copies, it isn’t a new edition, it’s just a new printing.

If, however, the pages are substantially modified, or the book is reformatted, such as for printing in paperback, then the printings in this new format will be a new edition. Note, though, that it may not be designated as a second edition (or third or fourth), and instead may be called a first paperback edition, first US edition or Penguin Classics first edition. Serious collectors typically consider these last inferior to the cherished first edition, first printing.

Depending on the publisher, the number line might also indicate the year the printing was done, like 2 3 4 5 6 93 92 91 90. This reveals that this second printing was done in 1990. Much like with the print run numbers, if the book is printed again the following year, the 90 would be removed, leaving the year part of the string as 93 92 91.

Moreover, if the publisher contracts with an outside company to do the printing, that company may be indicated in the number line as well; in this example, the number line shows Melissa’s Printing Company was hired to do a third printing in 2016: 3 4 5 6 7 8 9 10 MPC 19 18 17 16.

In addition, some publishers prefer other kinds of lines; for example, Anness Publishing uses a number line that alternates its digits as 1 3 5 7 9 10 8 6 4 2, where a second printing would read 3 5 7 9 10 8 6 4 2, and a fifth printing would look like 5 7 9 10 8 6. This particular schema is used to keep the number line relatively centered over multiple print runs.

Further demonstrating the lack of standardization across publishers for the printer’s key, the publishing giant Random House has indicated its first edition, first printing with the words first edition but with a number line that begins with 2 (as opposed to 1) such as 23456789; but, it uses this same number, just without the words first edition, to indicate a second printing.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

• Why Old Newspaper and Book Pages Turn Yellow
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• When People Started Burning Books
• Why There Are Bibles in Hotel Rooms