It's so easy to take things for granted, to assume they have been there for ever. For example, if you want to know how a tennis player's career is progressing, then you simply look at the Emirates ATP rankings. Prior to their introduction in 1973, you would probably still have known who the top singles players were. However, for the doubles, maybe not so much.
That changed in early March 40 years ago when the singles listings, which already included more than 300 players, were expanded to include the pairs game. It's also interesting to note that, back then, the entire ATP full-time staff numbered four! Now, such information is simply taken for granted, always at our fingertips, thanks to actions taken more than four decades ago.