Minecraft wiki entry for Clock, associated text: When the input turns off, the redstone torch initially "charges" the fader loop at signal strength 14 at the dust next to the block (the signal strength declined by 1 getting there from the torch). There are two comparators in the loop so each cycle takes 2 ticks, and the signal strength declines by 1 each time through the loop, so the fader loop remains charged for 28 ticks. One tick later, the redstone torch turns back on, re-powering the fader loop (it stays on for 2 ticks so it overlaps the fader loop's on time by one tick).