In notation, the short line used under the basic tone symbol is called the time reduction line. Its function is to shorten the sound value. That is, the duration of the original note is shortened by half for each additional time reduction line. If you add a time decreasing line under the quarter note, it is called an eighth note, which is equal to half of the quarter note; Add a time reduction line under the eighth note, called the sixteenth note, which is equal to half the duration of the eighth note, that is, equal to a quarter of the quarter note. I am an analogy.