Stack training requires a radar that can measure swings without ball impact.  Not all radar devices have this capability. 

At TheStack Baseball, we analyze radar devices that track training swings. This information is then used by TheStack Baseball App to account for any bias in speed measurements that are associated with our hardware design. What does this mean to you? If your radar measures with a bias, our smart algorithms adjust for it and accurately calculate your eSpeed and Distance Potential regardless of which device you are using.

When calculating eSpeed, we use your Stack Bat training speeds to estimate the speed of the sweet spot on your gamer bat based on the properties you provided in the profile.