An optical disc having marks for dispersed addresses that can be easily detected with high precision. A first and second supply line and a first and second discharge line of each of the first and second fluid channels, respectively, are connected to first and second meter-in control valve and first and second meter-out control valves, respectively. Subsequently, a second subsample may be ashed at low temperature to remove cellulose and refluxed with a concentrated acid followed by refluxing with a base and rinsing with deionized water to wash away gypsum, vermiculite and other soluble components. For example, when an instruction to start an event-data collecting process is received, a control unit initiates the event-data collecting thread.