Systems for retaining a replaceable part within an image display device are provided herein. The casing may be formed long between a portion having the reel and the opening portion. The engine system further introduces to a combustion chamber of the engine system and combusts therein the first fuel and the second fuel during high temperaturespeed conditions. The system is equipped with a mechanism for detecting movement of the user from the first microcell to one of the immediately adjacent microcells.