Gene Block, a professor of psychiatry and biobehavioral sciences at University of California, Los Angeles, and colleagues found that by middle age, the signal the master body clock in the brain sends out to other internal clocks to help resynchronize the different processes gets weaker.
The 4 o'clock spot is a Master button (for saving settings and quickly returning the center dial to its main volume control), and 6 o'clock features a half-dozen blocks that correspond to your virtual surround speakers.