hello Marco, clearly the manual is the reference N.1 however there is some learning curve and may be you need some guidance. As a start you need to know that AI Expansion Units setting has to be done via available OUTPUT channels in your PLC, in the same manner input AI readings shall be done via available INPUT channels. This is the main difference compared with an AI embedded in your PLC. However in your case, I see another Expansion Unit directly attached to the PLC so it will consume its own IO Channels and you have to take it into account when you are programing your AI module. Speaking of Expansion module, please note that they are channel consumer, AI/O or Boolean I/O cahnnel there is not difference, so if you have a module to the left of your AD42 keep in mind that this is consuming channels that you cannot made avaialble for other modules so you should study also this module manual. Finally, when you made your AI avaialble and converted into HEX you need to scale it in engineering units via SCL, SCL2 or APR. Experienced users prefer APR because is BCD free but is just matter or personal preference. Just in case, there is another similar issue in the forum so you may check it out.