Spent the morning on the arm-aligner threshold again. 15° felt right on my wrist, completely wrong on my brother’s — smaller wrist, faster relaxation snap, false triggers on almost every third gesture.

Options on the table:

• Fixed threshold, tuned per-user in a settings screen
• Auto-calibrate from a few seconds of idle baseline, CGM-style
• Percentile of observed range instead of an absolute degree value

Going with the second one. Rough shape:

baseline := sampleIdle(3 * time.Second)
threshold := baseline.roll ± NEUTRAL_BAND

Prototyping tonight instead of pushing another magic number.