I tried this yesterday and used this video for it: http://www.youtube.com/watch?v=F3JJOFzIV4s It said 92 mph when I calculated it. But I wonder if this is close to being accurate. There are a few things that seems too inexact..for one, you have to "approximate" where you are standing on the court when you serve. Second, you approximate where the ball lands. The app may measure accurately the time it takes for the ball to go from racquet impact to court impact, but the exavt distance the ball is going seems estimated. Also, it doesn't take into account exactly where you strike the ball when serving. Some guys impact the ball 2 feet into the court and some hit it from behind the baseline. I guess its a fun app to mess around with, but it probably has a +- of around 5 mph on accuracy because of these inexact parts of the measurements.