Our THC does something called Axis Override.. It uses a fake or false motor to handle the Jog velocity moves of your Z axis. In rare cases, some may want to have a separate Steps per Unit for their THC. When your THC tells Mach it wants to go up or down, you get this Axis override command to command Z in its stead.  All this logic is handled inside of your M3 macro. So when you call M3, it will start looking for the up or down commands after we have ARC OKAY and we get past to the "Cut" Sequence of the torch.