Metronome
The metronome made it possible for a composer to show the performer what speed he wanted. If the composer writes at the top of his music: Crotchet (quarter note) = 76, for example, then the metronome can be set at 76 and it will tick at the right speed for that piece of music. Sometimes they write "MM76". The "MM" stands for "Maelzel's Metronome". Beethoven was the first composer to use metronome markings, but he often gave very fast speed indications, and some people wonder whether he made mistakes or whether his metronome worked properly.