Even if you start the discs at the same time, they won't finish at the same time. The timing skew on CD players was such that you'd actually accrue a few second

Even if you start the discs at the same time, they won't finish at the same time. The timing skew on CD players was such that you'd actually accrue a few seconds of error over the course of the songs. I think I remember reading that this even surprised the Flaming Lips.