Apple LaserWriter 12/640 PS - Manual (Page 221)

5 Distribute the toner powder by gently rocking the cartridge back and forth.
6 Firmly pull the tab directly away from the cartridge to remove the sealing tape.
WARNING Be sure to pull the tab straight out of the cartridge. Don’t pull
too quickly or at an angle—either might damage the toner seals within
the cartridge.
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