%mch
From Zenitel Wiki
The %mcm macro is related to the Multiconference feature. The macro will return the first station-channel (phy) related to the mixer_station (phy) that is member of the conference (no 1-99).
Syntax
Format: %mch(mixer_station,conference)
Example
$CONF_TALK N%mch(1,%tnsf(8201)) - Will give talk back from the mixer channel listening to conference 1, on mixer station starting at physical 1.