IOCP4FSX relation between (custom?) event-id's and local gauge variables

Hello,
does anybody know how the relation between (custom?) event-id's 3000-300x from iocpoffsets.xml in the group "EXTERNAL_GAUGES/737-800/EFIS_CONTROL_PANEL" and (local) gauge variables like L:DISPLAY_SCALE works in iocp4fsx?
I tried to find some information at www.iocpserver.com, but there is nothing about that on the internet.

Thanks,
Thomas