Scoring in Tennis can be weird for beginners. From the moment a game starts, nothing really makes sense. Here is the possible origin behind the tennis scoring system.
The origins of the 15, 30, and 40 scores are believed to be medieval French. The earliest reference is in a ballad by Charles D’Orleans in 1435 which refers to quarante cinque (which gave rise to modern 40) and in 1522 there is a sentence in Latin “we are winning 30, we are winning 45”. The first recorded theories about the origin of 15 were published in 1555 and 1579. However, the origins of this convention remain obscure.
It is possible that clock faces were used on court, with a quarter move of the hand to indicate a score of 15, 30, and 45. When the hand moved to 60, the game was over. However, in order to ensure that the game could not be won by a one-point difference in players’ scores, the idea of “deuce” was introduced. To make the score stay within the “60” ticks on the clock face, the 45 was changed to 40. Therefore, if both players have 40, the first player to score receives ten and that moves the clock to 50. If the player scores a second time before the opponent is able to score, they are awarded another ten and the clock moves to 60. The 60 signifies the end of the game.