Weight-collecting scale made by Joseph & Edmund Ratcliff of Birmingham, England, and patented by R. Willis in 1840. The letter plate is supported by a half-roberval system. When a letter is placed on the plate, the beam tilts and collect the first of five weights stored in slots in the frame. If necessary, it continues tilting to collect further weights until equilibrium is reached. Brass on a marble slap with an ornate ormolu under frame. There is another version on a wooden base. Length 10"

Another model is smaller and has only three weights. Other designs using this principle are known. ( Post Office Scale from Germany )