Sony VGN-SR490DDB - Manual (Page 70)

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Using Your VAIO Computer >
Using Fingerprint Authentication
2 Swipe your finger perpendicularly across the fingerprint sensor.
!
Place your fingertip flat in the center of the fingerprint sensor.
Scan your fingerprint from the top joint of the finger to the fingertip.
Keep your finger in contact with the fingerprint sensor while swiping.
Fingerprint registration may fail if you move your finger too fast or too slow. Let the fingerprint sensor take about one second to scan your fingerprint.
You may not be able to register and/or have your fingerprint(s) recognized if your finger is excessively dry or wet, wrinkled, injured, dirty, etc.
Register more than one fingerprint in case that the fingerprint sensor fails to recognize the fingerprint.
Be sure to clean your fingertip(s) and the fingerprint sensor before swiping in order to keep good recognition performance.