Golf swing tracker teams learned calibration matters more than sensor fusion math

Developers building a golf swing tracker using a 9-axis IMU on a TV box found that agreeing on what zero means mattered more than refining the fusion algorithm. A mounting mismatch alone caused 11 degrees of club face error, so they added a mechanical reference key, tagged each report with its bracket revision, and re-zeroed at every session start. Cheap gyros drift with temperature, so the team re-estimates bias during quiet periods to avoid phantom rotation. To meet a 120 ms sensor-to-screen budget, they moved heavy processing to the box, deferred storage writes, and preloaded assets. They also dropped metrics such as swing plane angle and tempo ratios that proved unstable across mounts.