Finger choice
- Index or middle finger is standard — larger, flatter surface than the ring/pinky, easier for users to place consistently.
- Skip the thumb if you can — it's harder to center and has more print variance.
Placement
- Finger should lie flat, not on its side or at an angle — the pad should sit dead center on the sensor glass.
- Full pad contact matters more than pressure. Fingertip-only placement is the #1 cause of low-quality captures.
- Keep the finger still during the 1–2 second scan window — motion blur is the second most common failure.