Vintage postal scale also known as pendulum scale. Historical use: These instruments were once used in post offices to weigh letters to calculate the cost of postage stamps. Mechanism: The scale is based on a pendulum: When an item is placed in a bowl, the scale moves along a graduated arc indicating its weight. Design: This item is usually made of cast metal, and sometimes includes an enamel or porcelain arc with numerals. Manufacturers: German companies such as Philipp Jacob Maul were prominent manufacturers of these models in the early 20th century.