Abstract: A light pickup 4 is adapted to receive reflected light from a disc 1 and to input a signal into a determination means 12 while moving in the radial direction of the disc 1. The determination means 12 not only determines the current position of the light pickup but also calculates the time required for the light pickup 4 to move until reaching the signal-recording inner circular end of the disc, on the basis of the signal from the light pickup. The determination means 12 determines that no disc is set when there is no reflected light from the disc. The determination means 12 determines the size of the diameter of the disc 1 on the basis of the current position of the light pickup 4. The disc player has a structure in which it is not necessary to provide a switch for detecting the signal-recording inner circular end of the disc, a sensor for detecting the size of the diameter of the disc and a sensor for detecting whether or not the disc is set.

Abstract: A hit indicating system in an aerial firing practice target to be towed comprises parallel connected resistance circuits the combined resistance of which is varied when any of the circuits is cut by a bullet, and this variation activates an ignition control unit comprising a differentiation circuit, a logic circuit, an output circuit, and optionally, a waveform shaping circuit, to transmit signals causing signal tubes to operate in sequence to emit flares or smoke preferably of significantly different hues indicating sequential hits to enable visual observation from aircraft at relatively remote positions.