Postal scales come in many forms and operating designs, but most are simple balances and pans on a frame mounted to a wood platform. They are usually made of brass or nickel brass. The wood base invariably has recesses to accommodate round wafer weights, which are often nested or stacked, or, less commonly, rectangular weights. If metal, a small ring may be attached to the base in which the weights are stacked. Postal scales can be plain or works of art with inlay designs in the pans and ornate frames or have a creative design in the platform. Some postal scales are self-indicating. For example, the Depose counterpoise scale is fitted with a weighted pendulum that moves along a graduated arc, or alternatively the arc scale moves beside the pendulum indicator when weight is loaded. Spring loaded postal scales of various types largely superseded scales with weights by the 1950s, at least in 1st world countries, which in turn were largely replaced by electronic scales during the 1970s. Self-indicating scales are relatively inexpensive compared to electronic scales and still available.