A multi-stage reactor system for preparing biodiesel is used to increase efficiency and yield and reduce impurities. The apparatus includes an input correction unit that corrects a difference between characteristics of a first input sound input from a first input apparatus and characteristics of a second input sound input from a second input apparatus. The base plate is formed with a generally elliptical through-hole, while the fastening plate is provided with a locking protrusion to be fitted into the through-hole of the base plate when the base plate and the fastening plate are superposed on each other. The processor is configured to communicate, through said interface connector, via a plurality of communication protocols. It also relates to a process for making such high melt swell polymers as well as for covalently crosslinking other polar copolymers including non-neutralized acid copolymers and non-polar alpha olefin polymers by using a minor amount of metal acrylate, particularly sodium or zinc acrylate. The optical position detection device detects the position of the input based on the location of the interrupt.