Minecraft wiki entry for Hopper_clocks, associated text: Hoppers usually have an 8 game tick cooldown between transfers (4 redstone ticks). The command block gets activated 2 game ticks after the item enters the back hopper (due to the comparator delay), so setting X to 6 would produce no change. Thus, this clock will have a clock period of 8 game ticks for the front hopper, plus X+2 game ticks for the back hopper, for a total of X+10 game ticks (X/2+5 redstone ticks).