Before the open era of tennis arrived in 1968, rankings for amateur players were generally compiled either for a full year of play or in September following the U.S. Championships. Professional players were ranked by journalists, promoters, and players' associations either at the end of the year or in the summer when the world pro tours finalized. There were also point ranking systems attached to professional tournament series in 1946, 1959, 1960, 1964, 1965, until open tennis in 1968. Even for amateurs, however, there was no single official overall ranking that encompassed the entire world. Instead, nation rankings were done by the national tennis association of each country, and world rankings were the preserve of tennis journalists. It was only with the introduction of computerized rankings in the open era that rankings were issued more frequently than once yearly, although interim rankings were reported in those years which had point series. Even the end-of-year amateur rankings issued by official organizations such as the United States Lawn Tennis Association were based on judgments and not on mathematical formulas assigning points for wins or losses.