Until the 1976 Summer Olympics no-one had ever achieved a perfect score in gymnastics.
Indeed, the scoreboard only had three digits, to display scores such as 9.50, or 9.85.
Nadia Comaneci, a 14-year-old Romanian gymnast competing at her first Olympics was to change that.
In her opening event in Montreal, her 30-second routine on the uneven bars was so perfect that the judges awarded her a 10, only to discover that there was no way to display the score on the board. To the initial confusion of the crowd, the board flashed up "1.00" instead.
Forty years on from the competition, Nadia Comaneci tells Witness about her extraordinary achievement.