Every miner had his own personal number. This number was on his tag(s), which was used to register his attendance. There was a different shaped tag for each shift. In the Dutch State Mines, for example, the tags for the morning shift were round, a triangular shape was used for the afternoon shift and square shape for the night shift. Every miner had his own lamp which also had his personal number on it. If you want to know more about the personal number, click here to read more (Dutch).