Postal scale

Brass postal scale with mahogany lid and weights: England, early 20th century.

These are small Roberval balances used to weigh mail or, more precisely, to determine the applicable postage rate. The smaller, usually circular, left-hand pan holds the characteristically marked weights (the "bucket weights"), while the right-hand pan holds the letter.

When not in use, the weights are stored in the wooden base, which is approximately 20 centimeters long.