Minecraft wiki entry for Hourly_clock, associated text: A 75-clock has half the repeaters of a full circuit, and one more inverter for the signal telling you that an hour has passed. After the basic circuit is built, add 74 more repeaters to the chain and connect then end of the chain back to the inverter. then, before the inverter, have a wire branch off and lead to another inverter, which in turn leads to a note block, or a sequence of note blocks. The second inverter is needed for this reason: As the clock only has 75 repeaters instead of 150, the note blocks need to go off only once every 2 cycles. And, a clock circuit has 2 sequences. The first is a power up, in which the repeaters all turn on; the second is a power down, where the repeaters all turn off. This cycle repeats endlessly unless interrupted by a broken chain or a save and quit. Sleeping in a bed can cause clocks to get off-time. A reset system that loses very little time can be made using pistons.