AFTE Store - “Criteria for Identification” or “State of the Art” of Firearm and Toolmark Identification

In firearms and toolmark comparisons one of the most profound conclusions you can reach is that you have individualized a “toolmark” as having been made by a specific tool to the exclusion of all other tools. What we are really saying when we make this statement is that the chances that another tool edge or working surface could have generated such a similar combination of class and accidental, and therefore individual, characteristics is so small that for practical pruposes it can be disregarded. What is the rational, either theoretical or empirical, which allows us to make identification of this nature?