In playing with these, I've found that there are a lot of ways to get an inaccurate reading - the #1, however, is if you have a catcher that stabs at the pitch (50mph becomes 60mph), or falls away from the pitch (60mph becomes 50mph). If you overcome that problem, the market research that I've seen says that most of these type of products tend to register 3-5 mph either side of the actual.