Sekonic SR-3500 Operating Manual page 77

Options Stacker unit Stacker unit preparation
5.
Lift the cartridge case lever and insert an ink cartridge.
Note)
Align positioning pins (2 places) of the ink cartridge with the positioning
holes (2 places) of the cartridge case.
6.
Lower the cartridge case lever to lock the ink cartridge.
7.
Install the printer in the stacker unit.
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Lever
Positioning holes
Align positioning pins