Canon imageRUNNER ADVANCE 4551i Service Manual page 329

2. Check the perpendicularity at the leading edges of the test chart and copy.
Measure dimensions A and B on the test chart and dimensions A' and B' on the copy. If (A-B) is not same as (A'-B'), go step
3 and following steps.
A
Feed direction
B
A'
Feed direction
B'
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Test chart
Copy
5. Adjustment