Crest Audio V12 Owner's Manual page 41

master modules
—M1, M2
alternate output features
solo switch
Will illuminate when manually selected in one of the consoles many Solo
modes. Controls within the master section determine if this switch will
sample signal pre or post level control.
The SOLO system is designed that if the Alternate output is soloed, it will
display its contents on the Solo meters, but it will not feed Solo signal to
the Alternate output section, avoiding a potential source of a feedback
loop.
write-on strip
Provides an area to label the alternate outputs usage.
p. 41