Barlines Barlines Barlines are vertical lines that indicate the beginning and end of measures. The only fixed standard is that generally barlines are the thickest, staff lines are thinner, and stem lines are the thinnest.
Barline thickness varies from engraver to engraver.
The barline connects the top and bottom lines of the staff. A systemic barline, which connects the beginning of two or more staves, is used. Then the connecting barlines continue throughout the piece. A systemic barliine connects the 3 staves. Then the barlines for the piano part are connected, and the vocal part is treated like single-line music.