If you do music, you may have seen in the notes at the beginning of a musical work, or such like instructions: M.M. = 72 or = 108, a = 60. They are put directly after the verbal symbol rate and indicate, too, though more accurately, on the tempo. For example, MM = 72 means that the music must be performed with a speed of 72 half notes per minute.
How to find this speed? This answer letters M.M., meaning "the metronome Malala".
Metronome - a device equipped with a clockwork mechanism that accurately counts the duration (like parsing a new play, you sometimes think: time-and, two-and, three-and), while in the right - given speed. It was invented in Vienna mechanic I. N. Menzel. His name this device is called. It looks like a wooden pyramid, with one side panel is removed. Under it fixed bottom pendulum with a sliding weight, and the pyramid - scale with numbers. If you move the weight on the pendulum, in accordance with the order against any number on the scale to set the pendulum swings faster or slower and clicks, like the ticking of a clock, said desired fraction of the clock cycle, the higher the weight, the slower it goes the pendulum; if its set in the lowest position, you will hear a frantic knock.