Panasonic CF-VDW07CRFM User Manual

The sensor used in the fingerprint scanner creates an image based on the
way in which the sensor comes in contact with the finger.  The image is
affected by the condition of the skin on the finger, and by the pressure
applied by the finger on the sensor.
At low temperatures, the finger tends to be dry, and the image comes out
very light, while at higher temperatures the finger tends to be moist, so
the image is darker.  Furthermore, if the finger is dry, it may take longer
to create the fingerprint image.
If the fingerprint is too light or dark, refer to the following.

Is finger too dry, or is skin of
finger rough or chapped?
Breath on the finger to warm it
and provide moisture, then press
down firmly on the sensor.

Is there perspiration on finger, or
is finger wet?
Wipe finger with a handkerchief
or tissue, and touch the sensor
more lightly.