Aces amount is an unprecise information
Every time the player severs an ace in tournaments with a large crowd, we hear the ovation and feel the enthusiasm of the fans, lovers of tennis. And it is really nice to see someone do a fast serve over 200 km/h (125 mph) where the opponent can´t reach the ball. Sometimes the serve is not too fast. But it has such an angle that again the opponent can´t reach it. But for the statistics analysis the ace and the non returned serve, where the opponent touches the ball but can´t get it back in court, has the same classification. For coaches and players, to do a fine interpretation of a player serve, it would be much more important to have a rate of non returned services, independent of total amount of aces. For both services, first and second. Some players have an incredible ability to do a better second serve than the first serve. They manage to get such an angle and so much spin that their second serve is more difficult to return than their first service. An example of excellent second serve was Pete Sampras, who did not consistently serve over 200 km/h. I am not saying that he had a second serve better than the first one. But he could change the direction of the serve without changing the toss position. Even though he had an incredible first serve, his second serve was fantastic too. Coaches, try to stimulate your players to do different serves from the same toss position. It is possible and it works. Also, pay attention to the non returned serves rate. It can make a big difference on the serve analysis.