Acme egg grading scales were produced by Specialty Manufacturing Company, St. Paul, Minnesota, founded by William Boss in 1900. Specialty's first products included a grass catcher for a lawn mower, clothesline reel and garden hose reel followed by several other items, including the Acme egg grading scale. In 1922, Acme inventor N.E. Chapman filed for a patent for what he referred to as an egg grading device. The patent was granted in June 1924. Early Acme egg scales were of aluminum construction. Later models had tin bases that tended to rust over time. The scales work on the weight-lifting principle. Each scale has nine fins that are lifted to determine an egg's weight. The weight of the egg lifts individual fins that rise until the precise weight of the egg is determined.