First, make sure you are comparing apples to applesPlease compare eSpeed to your driver speed when not hitting a ball. This would be the case in the Baseline driver swings. Prior to speed training it is common for clubhead speed to be much slower without ball contact.Please ensure you are comparing speeds measured with the same radar.  For example, the radar you use for Stack training may read differently from a radar you used during a recent club fitting session.There are a few reasons why your driver speed might be different from your eSpeed  You are actually swinging your driver differently than TheStack.Your driver length is not the same as what you’ve entered in your Profile information.The radar is picking up your driver speed slightly differently due to its material make-up and shape. TheStack and driver are not moving through the same location in space relative to the radar. Since TheStack is shorter, you will need to stand a bit closer to the target line. Clubhead speed is a function of linear grip speed and angular grip speed. If you have high linear grip speed relative to angular grip speed, then your eSpeed will tend to be over estimated. Watch this video for details  Influence of Driver Length on Clubhead Speed