Fujitsu FI-4860C2 Operator's Manual page 298

- The deviation in the amount of the light transmitted through background areas
must not be less than 10%.
HINT
HINT
●AP-4
The type and the conditions of document and the conditions sometimes
cause the double-feed detection rate to drop.
When the overlapping check is specified, the paper sheets which contact
closely each other, such as electro-statically charged paper, can result in the
miss-detection of double-feed.