These are mechanical clocks, meaning they have to be wound in order to continue running. The weights are powering the clock and will slowly fall to the ground. The loose end of the chain is then used to pull the weights back up to the clock. With 1-Day clocks this needs to be done once a day. The clock will sound every thirty minutes. On the top of the hour, the bird will "cuckoo" the time and at the bottom of the hour, the bird will "cuckoo" once.