Minecraft wiki entry for Clock, associated text: Even torch based 5-clocks can be made more compact, as with designs B and C. However, these have fewer places where repeaters can be inserted without using more space. Using this method, 1-clocks and 3-clocks are possible, but these are unstable and erratic as the torches regularly "burn out". As with the basic clock, the compact clocks can be extended by making the chain of inverters longer, or with repeaters. A 5-clock can also be made vertical, as in G.