Ricoh D124 Detailed Descriptions Manual page 50

 The sensors to the left of center (set sensor position "0") detect B series (Metric)
or Architecture (USA) sizes.
 The sensors to the right of center (set sensor position "0") detect A series (Metric)
or Engineering (USA) sizes.
 If the original set sensor is the only one that detects paper, the machine detects an
A4 or 8 ½" "A" size SEF original.
D124 44 Detailed Descriptions