Mathematicians and scientists seldom rest easy when the numbers are not right. The search for understanding is never far from mind. In many ways, this is why mathematics is so much fun. Similarly, conductors and musicians, who immediately recognise wrong notes, are perplexed by Beethoven’s metronome markings. Some of his tempo markings, even on many of his most popular classics, have been considered so fast as to be impossible to play. What is the problem? Why?