Printer's key

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A copyright page with the printer's key underlined. This version of the book is the eighteenth printing.

The printer's key, also known as the number line, is a line of text printed on a book's copyright page (often the verso of the title page, especially in English-language publishing) used to indicate the print run of the particular edition. The convention appears in titles published around the middle of the 20th century; it became common practice after 1970.[1][2]

An example follows:

1 2 3 4 5 6 7 8 9 10

This is how the printer's key may appear in the first print run of a book. Numbers are removed with subsequent printings, so if "1" is seen then the book is the first printing of that edition. If it is the second printing then the "1" is removed, meaning that the lowest number seen will be "2".[3]


Usually, the printer's key is a series of non-repeating numbers or letters. However its structure or presentation is not uniform, as shown in the following examples.[4]

The series may be in descending or ascending sequence:

10 9 8 7 6 5 4 3 2 1
1 2 3 4 5 6 7 8 9 10
a b c d e f g h i j k

In some cases, rather than follow in unidirectional sequence, the numbers may alternate from left to right:

2 4 6 8 10 9 7 5 3 1

In other cases, number lines may include a date segment consisting of two-digit year codes:

2 3 4 5 6    73 72 71 70

This indicates a second printing (or second impression) and that it occurred in 1970. Specifically, it is the particular imprint's second impression of the edition.

When the publisher outsources the printing to a contractor, a code identifying the contracting printer may occasionally be shown:

3 4 5 6 7 8 9 10   APC   00 99 98 97 96

The hypothetical printer's key above means

  • third printing
  • printed in 1996
  • contracted to Acme Printing Corporation.

The examples above are not exhaustive, and other key configurations may be used.[5]

First edition vs. first printing[edit]

Bibliographers usually define a first edition as all printings from substantially the same type setting, no matter how many printings are done. Book collectors tend to define first edition as the first printing of the first edition.[6][7]

Why numbers are removed rather than added[edit]

With each successive reprint, the publisher needs to instruct the printer to change the impression number. In practice, if the plates (in offset printing) have been kept, a number can be erased, but nothing can be added. In this arrangement, all the printer need do is "rub off" the last number in sequence. Changing only the outer number requires the fewest possible changes to the page of characters, which means the smallest possible charge to the publisher.[1] In the days of letterpress printing, where each character was a metal block, all the printer had to do was to pick out the relevant block(s) from the "sheet"; the remaining stack of blocks, which had been laboriously laid out when the page was first set up, could then be inked for the reprint.[8] In the case of a Linotype slug, the lowest number could be filed off and the slug reused.[10] For offset printing with metal plates, the number can be erased without damaging the rest of the plate. In each case, the change is minimal.[11]


  1. ^ a b Boutell 1949, p. 26, § "Thomas Y. Crowell Company" ¶ "1947 Statement".
  2. ^ Ahearn & Ahearn 2011, § "First Edition Identification". Retrieved 2022-08-24 – via Google Books (limited preview).
  3. ^ Stop Counterfeit Books 2022.
  4. ^ Rennicks 2021, § "How Can You Tell if a Book is a First Edition?"; Ahearn & Ahearn 2011, "First Edition Identification By Publisher". Retrieved 2022-08-24 – via Google Books (limited preview).
  5. ^ Stop Counterfeit Books 2022, § "D".
  6. ^ Boutell 1949, p. [ix], § "Explanatory note to the Original Edition".
  7. ^ Carter 1995, pp. 84–85, § "Edition and Impression".
  8. ^ Levy & Mole 2017, pp. 17–22, § "Making Printed Books".
  9. ^ The Inland Printer 1899, p. 745; The Linotype Bulletin 1918.
  10. ^ In theory; linotype operators sometimes used files (and other tools) in order to make fine adjustments.[9]
  11. ^ Duncan & Smyth 2019, p. 64.