Yamaha MMP1 Operation Manual page 46

REF Tap to call up the reference level, and then
hold this down for at least two seconds
(until the indicator flashes) to store the
current Monitor Level value as the
reference level.
DOWNMIX Tap to turn the Downmix audio output on
(green) or off.
Turn this on to send Downmix L/R outputs
to the Main Monitors 1 and 2 while muting
outputs from Main Monitor 3 onwards.
NOTE
This button is disabled when the Cue
output format is selected as the audio
being monitored.
Here you can display and load User Assignable functions.
Use the MMP1 Editor to configure settings.
Here you can display Monitor Matrix Out meters. Values
less than -20 dB are displayed in green , values less
than 0 dB in yellow , and values equal to or above 0 in
red . Peak hold circuits are not displayed.
4. Screens
MMP1 Operation Manual 46