Offsetting page numbers in an index

This requirement pops up now and then. The page numbers in an index need to be altered due to some unavoidable pagination change. Sometimes it can be legal requirements, or a revised edition of the book where a new chapter is added. We recently encountered the situation where the original edition of the book did not use roman numerals in the prelim pages, so chapter one was starting on arabic folio ‘11’. Using our automation software, we were able to fix the index page numbers so that chapter one started on folio ‘1’. It would have taken hours to mark-up.

The software works something like this:

• Expansion of number elision; 21–2 becomes 21–22.
• Specification of starting page; the page from which the pagination change occurred.
• Specification of the offset; the number of pages that were added or subtracted.
• Recalculation of the affected page numbers, using the specified offset.
• Number span contraction (elision); 31–32 becomes 31–2 (10–19 exceptions are automatically handled).

The software is effective in several common scenarios.

Renumbering prelims with roman numerals

The software works with pages with roman numeral folios – it's a handy feature. So, in the example where the book was renumbered with roman numerals in the prelims, any indexed pages prior to chapter one were assigned the correct roman numerals. Since chapter one previously started on page 11, the software changed all the index page numbers between 1 and 10 to roman numerals, and then all the page numbers from 11 onwards were decreased by 10. This changed the index such that chapter 1 was indexed as page 1 (= 11 – 10).

Removal of pages

In the case where the book is re-paginated due to some removal of pages, the range of indexed page numbers is constrained. This is a necessary feature since often the re-pagination will occur in the middle of the book. The software is told to start at a certain page number and work from there. For example, we can tell the software to change all the page numbers from page 100 onwards, decreasing them by 2.

Addition of pages

Similarly, it is possible to insert pages into the book, such as adding a new chapter into a revised edition. The algorithm must work in a slightly different way here. For example, let’s look at the scenario where a new chapter is inserted after page 200, and runs from 201 to 220. This would mean that all the indexed page numbers that were previously 201 would become 221, and so on. If we work forwards, then we would encounter 221 – changed from 201 – in the progression, and it would be increased to 241! Not what we want. The trick is to work backwards; from the last page number in the book to the point of change.

The software handles this scenario automatically, based on the provided offset. If the offset is a positive number – pages have been inserted – then the software knows to work backwards.

This utility can save hours of work, and remove the potential for error. Just as importantly, it opens up possibilities that might not have been considered due to time or budget constraints. If you would like to discuss the specific scenario for your project, do not hesitate to contact us.