Situation: A chest with a hopper on top of it.

When throwing an item on top of the hopper, making the hopper sucking it into the chest, will sometimes duplicate the item. This will need an increasing amount of that item retrieved from the chest. e.g. 1 diamond -> 1 diamond, 1 diamond -> 2 diamonds, 2 diamonds -> 3 diamonds, etc.
This works for both Survival and Creative.

I hope this is clear enough, because I am Dutch and my English is not that good.