The IAAF ratifies track and field world records if they meet their set criteria. The IAAF first published a world records list in 1914, initially for men's events only. There were 53 recognised records in running, hurdling and relay, and 12 field records. World records in women's events began in 1936 as more events were gradually added to the list, but significant changes were made in the late 1970s. First, all records in imperial measurements were abandoned in 1976, with the sole exceptional being the mile run due to the prestige and history of the event. The following year, all world records in sprint events would only be recognised if fully automatic electronic timing was used (as opposed to the traditional hand-timing stopwatch method). In 1981, electronic timing was made compulsory for all world record runs in track and field, with times being recorded to within one hundredth of a second. Two additional types of world record were introduced in 1987: world records for indoor competitions, and world records for junior athletes under 20 years old.