Minecraft wiki entry for Clock, associated text: When the input turns off, the redstone torch initially "charges" the fader loop at signal strength 15. There's only one comparator in the loop so each cycle through the loop takes only 1 tick, and the signal strength declines by 2 each time through the loop, so the fader loop remains charged for 8 ticks. The redstone torch then turns on for only one tick because it short-circuits itself (the torch does not burn out because it's held off most of the time by the fader circuit).