4.1.1 Staves and systems
A line runs down the left-hand side of all the instruments that are playing together, and the bar lines run through the staves.
Both of these signs show that these instruments are sounding simultaneously, and the whole group of staves is referred to as a system. If, on one page there is a section of music that only uses a few instruments, you may find two or more systems on the page separated by this symbol:
Watch out for these ‘tramlines’ as it is easy to miss a system especially if there is a small one between two larger ones. The example in Figure 3 is from the third movement of Mahler’s Symphony No. 1.