All sorts of calipers are handy for bookbinding, but today I am most enthusiastic about outside calipers. I happened to find a great one (left) at an antique market this past weekend. This is a tool that I use when making boxes. Box making is something that often goes hand in hand with bookbinding because many of the same materials and techniques are used. If you're working on book conservation, or repair, it is often wise to box a book so that it will be nice and safe!
The first thing you'll need to know before you start making a box is the dimensions of the object to be boxed. Calipers come in handy when measuring the thickness of old books. Books can warp over time depending on the various conditions they've "lived" through, so it's important to measure the thickness of the entire book and make a box to fit the thickest measurement.
My outside calipers have a screw mechanism that can be loosened or tightened until the tips are resting upon the thickest dimension of the object. Once the tips have found their position, the caliper can be removed from the object and then the distance between the tips can be measured with a ruler.
If you look closely at the tips of the two calipers, you can see that one pair is rounded while the others (the new pair) are flat and come to a point. I was excited to see this because it is so much easier to measure accurately between two flat tips than between two round tips. Although I should mention one word of caution. If you're using pointed calipers be sure that the tips don't scrape the book you're trying to protect!
Ah! Nothing like precise measuring! :)