The Particle Data Group (PDG) is a group of high energy physicists who, every two years, publish a summary of data of interest to other high energy physicists. Part of their task is to average the results of different experiments to create a "standard" number. They produce a small booklet which is intended to be carried around by said physicists, and includes such nice small additions as a ruler along the edge of some pages. This is from the Errata to the 1994 edition: The "centimeters" on the ruler on p. 227 of the Booklet are 0.97 cm long, because: a) The booklets were returned from the printer at 0.26 times the speed of light; b) A theorist is in charge of the Particle Data Group; c) The PDG feels it has the right to redefine anything it wants; d) There is a general decline of standards; e) There was an international conspiracy; f) It was a congressionally-mandated cost-saving measure; g) PDG gives you cm/inch than anyone else.
(From the "Rest" of RHF)