The invention relates to the field of anti-virus protection. A target frequency generated by a ring oscillator can be modulated by varying a supply voltage to the ring oscillator, thereby changing the target frequency. Using the scanned information, the metering device determines the Postnet bar code corresponding to the scanned information. The underdrain block is substantially greater in longitudinal length than a longitudinal distance between the upper orifices. The cured film has an epoxy-acrylic double-layered structure to give a high functionality, for improving properties such as weather-resistance, yellowing resistance, etc.