Canon 2/3 Hole Puncher Unit-A1 Service Manual page 29

2. When the punch horizontal registration sensor on the punch slide unit detects the paper edge (front) at the position according
to the paper size information received from the host machine, the punch slide unit stops at the punching position.
Paper
Punch Shift Motor (M302)
Punch Slide Unit
Punch Horizontal Registration Sensor (PBA301/PBA302)
Punch horizontal registration sensor 5
; detects the edge B5R paper
Punch horizontal registration sensor 4
; detects the edge A4R, LTRR and LGL papers
Punch horizontal registration sensor 3
; detects the edge B4 and B5 papers
Punch horizontal registration sensor 2
; detects the edge 11"X17" and LTR papers
Punch horizontal registration sensor 1
; detects the edge A3 and A4 papers
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2. Technical Explanation