Tennis player here..ummm... As legohead brought up, there are other things to consider like stance. I can see how this thing can be accurate if we had four of t

Tennis player here..ummm... As legohead brought up, there are other things to consider like stance. I can see how this thing can be accurate if we had four of them (ankles and wrists). This can show show most of the moving parts, can replay how the body moves (likely hand location and elbow extention), open vs close stance, how fast were moving from point A to point B. I don't know how they're measuring ball rotation, purely by the angle of an upward swing? Don't know if this is accurate. Is this an area it would suggest for improvement? RPM has a large range up to ~5,000rpm (Nadal). What would it even cosider optimal to make a shot? Don't know how the device would know if a ball would land in or not, is this even a major area of concern for the device? Pretty strokes are one thing, but unless the ball lands in, it doesn't matter. Depending on how accurate this device is (probably would need more than one bracelet per person), it can be used for any sports. More importantly, there's a possiblity to measure bad form and increased pressure on certain joints to prevent injuries. Looking forward to see technologies brings forth in the coming years!