Oki PT390 Manuel D'utilisation page 37

(5) After completing cleaning, reposition the roll paper, and close the
top cover.
Note : Take care not to dent or otherwise damage the platen roller.
A dent on the platen roller may result in incomplete printing or line feed
errors.
Note : Each time that the FEED switch is pressed, the platen roller is rotated by
1/12 of a turn.
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