Tennis game scores...15...30...40. Why these numbers? Do they have any significance?

As simple as this scoring appears, the running score of each game is described in a manner peculiar to tennis: scores of zero to three points are described as “love” (or “zero”), “fifteen,” “thirty,” and “forty,” respectively. The origins of the fifteen, thirty, forty scores are believed to have medieval and French roots. It is possible a clock face was used on court, with a quarter move of the hand to indicate a score of fifteen, thirty, and forty-five. When the hand moved to sixty, the game was over. Another explanation is that the scoring system was copied from the game sphairistike, which was played by British officers in India during the 19th century. That game’s scoring system was based on the different gun calibres of the British naval ships. When firing a salute, the ships first fired their 15-pound guns on the main deck, followed by the 30-pound guns of the middle deck, and finally by the 40-pound lower gun deck.[1]

The origin of the use of “love” for zero is also disputed; it is possible that it derives from the French word for an egg (l‘oeuf) because an egg looks like the number zero. “Love” is also said to possibly derive from “l’heure” or “the hour” in French. When stating the score, the server’s score is stated first. If the server (or the umpire) announces the score as “thirty-love,” for example, it means that the server has won two points and the receiver none.

http://en.wikipedia.org/wiki/Tennis_scoring