|A bar line is a vertical line drawn through a staff. The spaces between the bar lines are the measures defined by the time signature.|
|A bar line ONLY crosses between staves when the staves are played by the same instrument as in this typical piano-vocal score. The voice uses the top staff, the piano uses the bottom two.|
If a measure number or a rehearsal letter appears above a bar it refers to the following measure. Here letter A is at measure 2.|
|IMAGINARY BAR LINE
Meters with more than 3 beats have an imaginary bar
line in the middle to make the music easier to read.
|The top example could be written with a quarter note in the middle but the two-eighths are tied to show where the third beat is. Also the eighths are not barred across here.|
In 6/8 meter, the imaginary bar line is between the third and fourth beats.
In 5/8 the position may change according to the needs of the music.
In complicated rhythms an imaginary bar line may be employed between every beat as in the bottom example.