A data transmission device is applied to a network apparatus having an automatic crossover function, and is connected to a transmission control unit, such that the transmission control unit detects an operating status of the network apparatus and accordingly generates a control command. When a car is started, the second power output unit supplies power to the control circuit. The golf club head has a center of gravity located less than 1. to a temperature less than the melting point of the prepolymer. A system of controlling playback of digital media comprising a CE device having a secure clock and a license having a specified grace period disposed upon the CE device in which a digital media file governed by the license may be played for the grace period upon failure of the secure clock.