beam balance

Compares the mass of a body with that of another body of known mass (weight); when two pans hanging from a bar (beam) are in balance, the two weights are equal.

pan

Flat rigid support that holds either the body to be weighed or the weights.

beam

Horizontal metal bar that balances on a vertical axis and has pans hanging from each end.

weight

Piece of metal, such as copper or iron, of known mass that is placed on a pan to balance the scale and thereby assess the corresponding mass of a body.