The ASCU Gen 3 is so small that it fits inside a Version 2 gearbox where the trigger sits and it acts like a MOSFET system making your AEG fire with precision which could be compared with a PTW.
You can change firing modes such as:
Semi + 3 Rnd Burst + Full Auto
Semi + Full Auto (The usual)
Semi + 3 Rnd Burst (Like a real M16)
Semi Only (If skirmish areas have a certain rule)
It comes with a manual with direction on how to change modes. It's within the AIRSOFT SMART CONTROL UNIT USER MANUAL section under 'Coosing Fire Mode' which I guess means Choosing Fire Mode.
It's all computer controlled and has sector gear monitoring so one trigger pull is a complete cycle making it have a realistic, crisp trigger. It's compatible with LiPo, LiFe, NiMH,NiCd from 7.2 - 12 Volts.