What is “creep” in Desktop Publishing?

And how do you compensate for it?

Since we are in Halloween mood and creeping “monsters” knock at our doors asking for candies, I thought it was very appropriate to treat a subject such as our own creeping desktop publishing projects. Yet, if I have to tell the truth, I was just visiting one of my favourite sites about DTP and I saw an interesting article about creep and how to compensate it and I thought I should bring it to your attention. Jacci Howard Bear from About Desktop Publishing does a good job in answering a question of one of her forum members about the subject with this very useful article.

As Jacci says in her glossary:

In a saddle stitched booklet the bulk of the paper causes the inner pages to extend or creep further out than the outer pages when folded. When trimmed the inner pages are narrower than the outer pages, counteracting the creep.

Her glossary definition also shows an illustration and delves into further explanations, so I advise you to read it fully.

She then quotes the formula on how to compensate for creep:

Total pages in book, divided by 4 (for each 4 pager), times paper thickness. Take that number, and divide it by the number of flat sheets in your book. This number will be quite small, but will represent the amount that you should adjust each page’s outside margin, as you get closer to the center of the booklet. This works in most cases but using a folded, drilled, dummy of the actual job stock is best.

The full article has more information, which is not only interesting, but quite a must for someone who designs many saddlestitched booklets.