A peak programme meter (PPM) is a device used in professional audio for indicating the level of an audio signal.
In common with many other types of audio level meter, PPMs originally used electro-mechanical displays. These took the form of moving-coil panel meters or mirror galvanometers with demanding 'ballistics': the key requirement being that the indicated level should rise as quickly as possible with negligible overshoot. These displays require active driver electronics.
Nowadays PPMs are often implemented as 'bargraph' incremental displays using solid-state illuminated segments in a vertical or horizontal array. For these, IEC 60268-10 requires a minimum of 100 segments and a resolution better than 0.5 dB at the higher levels.
Many operators prefer the moving-coil meter type of display in which a needle moves in an arc, because an angular movement is easier for the human eye to monitor than the linear movement of a bargraph.
(Information from Wikipedia)
● adjustable reference level
● Left/Right and mid/side modes
● adjustable integration and return times
● Left/Right Phase Correlation LED
● adjustable Overs threshold and hold time