Roberval Balance

The Roberval balance is a weighing scale with two horizontal beams one above the other connected to two vertical beams supporting the weights to be compared.

Because the beams form a parallelogram, no matter where the weight is placed in the plates the balance works properly, compared to a simple beam scale which is sensitive to where the weights are placed in the plate. See it in action at https://www.youtube.com/watch?v=Bg7IBTMdyf0

Use this tool to compare the weight of any two small objects! It shows differences as small as 1 gram.

See https://en.wikipedia.org/wiki/Roberval_balance for more historical and scientific information about the Roberval balance.