In 1962, "3 Coin" became the best selling Williams machine with 1,100 units sold. One year later, "Skill Pool" sold 2,250 units. In 1964 Williams was purchased by the Seeburg Corporation. Its 1966 pinball machine "A-Go-Go", with its avant-garde 60s theme, sold a record 5,100 units. Early Williams pinball machines often included innovative features and pinball firsts, such as mechanical reel scoring and the "add-a-ball" feature for locations that didn't allow game replays. By 1967, pinball was in the middle of its so-called "golden age", and the number of pinball units that sold began to increase dramatically. Popular Williams pinballs included "Shangri-La" (1967), "Apollo" (1967), "Beat Time" (1967), "Smart Set" (1969), "Gold Rush" (1971), and "Space Mission" (1976).