Jolly balance

Jolly Balance is a type of scale that is used to measure the weight of things. It looks like a see-saw. On the long board of the see-saw, there is a tray to put the thing you want to measure. On the other end, there is a little container that holds weights. When you put the same weight in the container on the same side as the tray, the see-saw stays level - that is how you know that the two sides have the same weight. When you put different weights in each container, the side with more weight will go down lower than the side with the lighter weight, so you can tell which side is heavier.