Minecraft wiki entry for Zero-ticking, associated text: A 0-tick clock is made by putting two 0-tick block pushers facing each other and pushing a block between themselves, one line will appear on, while the other appears off, each has unique behavior, the "off" line is BUD-proof, while the "on" line allows for BUD pistons, and to set which is which, simply place a lever on the torch under the side you wish to be "on" and flip it twice, also this lever can turn it off.