What does "Display Peak Bar" and "Peak Hold" do?

"Display Peak Bar" provides a visual indication of the average peak value on the bar graph display, similar to what's seen on a graphic equalizer. 

The duration the peak bar is visible is configurable from a few seconds to a few minutes by adjusting the "Peak Bar" slider on the response tab. 

Alternatively, if you want the Peak Bar to be latched on and show the maximum value since the unit was reset, click "Peak Hold".