Toshiba GD-1151 Operator's Manual page 173

Duplex printing direction differs depending on the received original size.
1. Received LD, LG, LT, A3, A4, or B4-sized originals are printed so that they can be bound along the long edge
of direction.
2. Received ST, A5 or B5-sized originals are printed so that they can be bound along the short edge of direction.
( 1 )
Even when "Duplex Printing" is selected, one-sided printing will be applied to the following two
items.
1. Received fax documents which are relay-transmitted
2. Received fax documents which are sent to forward mailboxes
See the TopAccess Guide for details.
( 2 )
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