I have always advocated keeping a wide array of unusual and telling reference works on hand. This is one of the most chilling: it is a translation of original German records, mixed with eyewitness accounts, compiled by the former research head of the Auschwitz Museum. The memoranda and ledger entries dryly tell the horrors of industrialized, government-sanctioned, popularly supported mass murder. In a sense, this is one of the most truthful works about the 20th century. Running over 800 pages, you can slam someone who "doubts" the Holocaust happened over the head with it.