Either weigh produce directly, or put in a mixing bowl for liquids and set to 0 with that wheel. The tray can be also be removed for cleaning if something spills.
I was at a thrift store and saw a box labeled "kitchen wonder!" It was a mandolins from the 70's before America knew about them I guess. I still have it in the box, even though I'm usually a stickler for efficiency. It's just too enjoyable to have to pull out the "kitchen wonder".