An aqueous dispersion is prepared by subjecting acrylate containing a polyfluoroalkyl group and a polymerizable monomer containing no fluorine atom to an emulsification treatment in the presence of a surfactant and a polypropyleneglycol-based compound having a molecular weight of 250 to 5,000, followed by copolymerization reaction in the presence of a polymerization initiator. According to one aspect of this disclosure, a mobile device may be to modify audio playback in response to detecting an inclination of the mobile device with respect to a reference plane. The predetermined length mark signal measurement means detects a specific pattern including the 2T mark from a bit arrangement pattern of the information data, and measures the amplitude value of the 2T mark correponding only to the 2T mark included in the specific pattern. Further, content is provided to the user, utilizing the mood of the user. The size of the headband can be adjusted by a friction locking mechanism attached to its rear.