Martin Audio MLA User Manual page 417

MLA System
USER GUIDE
At this point the U-Net ports will not light on either cabinet as the second cabinet is not yet powered.
As you now have a couple of wheelboards you can start to neatly stack them, there are routed sections in the top of each
wheelboard designed to act as a castor cup to ensure that the wheelboards stack neatly and safely to take up the minimum
about of space backstage;-
MLA System User Guide V2.1
417