  Szilard's own answer to the dilemma posed by his engine was to presume that a demon could not operate the device continuously and reliably. He then tried to deduce where it must go wrong. He imposed the postulate that the second law must be obeyed and after eliminating all other sources of entropy production, he argued that a minimum entropy production occurs during measurement. The postulated second law is a modified one, requiring that the average entropy production in a measurement process must equal the average entropy reduction as a result of that measurement. Although Szilard did not identify a specific definition of entropy, it is clear from the context that he was considering the entropy of specific macrostates. The most significant aspect of Szilard's argument is, in effect, that if statistical mechanics is incompatible with the operation of untamed demons, then it is required that there be an entropic cost associated with the demon's acquisition of information.