The counting system
You have probably heard it … 15 - love, 30 - 15, 40 all. Why does the game of tennis use such a complex counting system?
There's actually two theories about the origin of this system. The first (and most acknowledged theory) is that in the early days of the sport, they didn't have the luxury of modern scoreboards which could be seen by everybody in the audience. To display the current score, they had to use something accessible and big enough to be seen from all places in the stadium.
The solution turned out to be a big clock. A local clockmaker provided the Royal Court with a new, large clock which hands could be moved from the front. To make it as clear as possible, the points were counted in quarters, 0 - 15 - 30 - 45 and finally 60. The server was represented by the big hand and the receiver had the small hand. Apparently the "45" was changed to "40" because it was easier to say (less syllabus) that "45".
The second theory is that the scoring has its origin in ancient numerology. During the middle ages, the number "60" was considered auspicious (complete), much like the number 100 is considered to be auspicious today. As a game was won with four points, the easiest and most convenient way of count was by 15, 30, 45 and 60.
The next time you're watching a tennis match live, turn to your neighbor and dazzle them with this nugget of knowledge. You will definitely get some "tennis-cred" for this one.