Humminbird CH Thirty II Operation Manual page 12

Insert the cartridge into the unit and press firmly against the front until it clicks into position.
Note: The cartridge will go in either way. Make sure your printed edge of the chart paper is
always at the bottom of the cartridge.
Rotate the stylus belt downward by hand to insure that the paper is installed properly and will not
interfere with the stylus. Replace the front cover and you are ready to operate.