Charles Babbage was twice asked by members of Parliament, “Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?” In his memoir of 1864 he said he could not rightly understand the confusion of ideas that would provoke such a question. For his engine he was right. But the question didn’t go away. In 1947 Richard Hamming at Bell Labs was only allowed the relay computer at weekends, so he would set a job running on Friday evening and come back on Monday to find that one error had made the machine abandon the whole thing. He reasoned that if a machine could tell an error had happened, it ought to be able to tell where, and put it right. In 1950 he published the codes that carry his name, where a few extra check bits let a machine find a single wrong figure and fix it. That answers the question with a qualified yes: one wrong figure, in a known place, if you planned for it in advance. Most good listening works like that. When someone knocks with a question that has a wrong figure in it, the right answer is often still there to be found, so long as I care more about what they meant than about what they typed.