Reassembling unknown broken objects from a large collection of
fragments is a common problem in archaeology and other fields.
Computer tools have recently been developed by the authors and by
others, which try to help by locating pairs of fragments with matching
outline shapes. These tools have been succesfully tested on small
collections of fragments. Here we address the question of whether such
tools can be expected to work for practical instances of the problem
(10<sup>3</sup> to 10<sup>5</sup> fragments). To that end, we describe
here a method to measure the average amount of information contained
in the shape of a fracture line of given length. This parameter tells
us how many false matches we can expect to find for that fracture
among a given set of fragments; and we show that outline comparison
should give useful results even for large instances.