Distinguishing B5 and EXEC Paper
When B5 or EXEC paper is loaded in the paper drawer, you can set which paper size to use for the operation.
1.
Press 
(Settings/Registration).
(Settings/Registration). 2.
Press [Preferences] → [Paper Settings] → [B5/EXEC Paper Selection].
3.
Select [B5] or [EXEC] for each paper drawer → press [OK].