A printer is arranged to engage a printer cartridge that is loaded with ink and print media. Information about the ink and print media is stored in an actuating formation formed on an external casing of the printer. The actuating formation typically comprises a two dimensional array of protrusions. The printer includes an array of capacitive sensors that is located so that upon the printer engaging the cartridge the actuating formation is brought to bear upon the capacitive sensors. By monitoring variations in capacitance of the sensors a processor internal to the printer is able to recover the information stored in the actuating formation and subsequently adjust printer operation accordingly.