Minecraft wiki entry for Clock, associated text: Pistons can be used to create clocks with a modifiable pulse delay without the use of pulse generators. In Java Edition pistons can be clocked in a fashion that leaves the arm extended only for the time required to push an adjacent block. However, note that if sticky pistons are regularly used this way (that is, as a 1-clock), they can occasionally "drop" (fail to retract) their block, which usually stops the clock. (Specifically, if the setup allows for a pulse less than 1 tick long, that causes a sticky piston drop its block. This can be useful, notably for toggles.) Piston clocks in general can be easily turned off or on by a "toggle" input T.