On the harmonica, some notes are produced by breathing out, while others are produced by breathing in. An exhale breath is indicated by the letter e and an inhale breath is indicated by the letter i. The following notation shows one octave of the C major scale played in quarter notes. The letters e and i indicate the correct breathing. The numbers under the breathing letters indicate the holes on the harmonica. Notice that the higher C can be played on both holes 4 and 5.