There is some debate as to how tennis gained its wonky scoring--you know: love, 15, 30, 40, deuce. Some say that it derives from a clock face that might have been used to keep score in the Rennaisance: 15, 30, 45, 60. "But wait!" you shout. "There is no 45!" It has been argued that "45" was shortened to "40" because it was easier to say. This may be true in French, (a language, I am told, which has a really odd counting system), but it certainly seems to be stretching it in English.
Others argue that tennis derives it scoring from a sphairistike (a game played by British officers in India) which named the scoring after the caliber of canon on ships.
The term "love" has obscure origins too, with various people making up etymologies as they go along.
As you can see, there is no clear history of either the game of tennis (which existed at least since the thirteenth century in some form) or its scoring. It is argued that early tennis (played inside on wooden courts) was a very different game indeed. Sphairistike, they would argue, is the direct predecessor of modern outdoor tennis.
So the fact is that the history of tennis is quite obscure. No doubt this is because people were much too busy playing the game than writing about it.