As yoshi said : it's a very old design. And a begginer design too :
knowing the transfer speed is 2.5 item/s you can create very precise clocks. All you have to do is link a comparator to the next hopper in the line.
A very precise hopper clock.
hopper 1 send items into hopper 2, and as long as there's an item into 1, 2 receive power.
At 2.5 item/second, if you put 10 items in 1, it will take 4 seconds to go into 2, and 16 to get all 10 items back into 1.
Play with it a little and you'll be able to make, for exemple, a 20 minutes long clock, with a hoven at the end that will cook your grown up chicken.