A continuous inkjet printer comprising: an ink cartridge receiving portion arranged to receive an ink cartridge and to allow passage of ink from a received ink cartridge to printing fluid conduits of the continuous ink jet printer; a solvent cartridge receiving portion arranged to receive a solvent cartridge and to allow passage of solvent from a received solvent cartridge to printing fluid conduits of the continuous ink jet printer; an ink supply system arranged to receive ink from a received ink cartridge and solvent from a received solvent cartridge and to mix the received ink and solvent to produce printing ink for supply to a print head; a first data reader arranged to read data indicating a quantity of ink within the received ink cartridge from an electronic data storage device associated with the received ink cartridge, said data reader comprising a plurality of electrical contacts arranged to make contact with corresponding electrical contacts of the received ink cartridge; and a second data reader arranged to read data indicating a quantity of solvent within the received solvent cartridge from an electronic data storage device associated with the received solvent cartridge, said data reader comprising a plurality of electrical contacts arranged to make contact with corresponding electrical contacts of the received solvent cartridge; and a controller arranged to generate update data usable to modify data stored on each of said electronic data storage devices (201, 301) and to modify data stored on said electronic data storage devices based upon said update data, such that data stored on each electronic data storage device indicates a respective updated quantity of fluid in said respective printing fluid cartridge. an ink cartridge receiving portion arranged to receive an ink cartridge and to allow passage of ink from a received ink cartridge to printing fluid conduits of the continuous ink jet printer; a solvent cartridge receiving portion arranged to receive a solvent cartridge and to allow passage of solvent from a received solvent cartridge to printing fluid conduits of the continuous ink jet printer; an ink supply system arranged to receive ink from a received ink cartridge and solvent from a received solvent cartridge and to mix the received ink and solvent to produce printing ink for supply to a print head; a first data reader arranged to read data indicating a quantity of ink within the received ink cartridge from an electronic data storage device associated with the received ink cartridge, said data reader comprising a plurality of electrical contacts arranged to make contact with corresponding electrical contacts of the received ink cartridge; and a second data reader arranged to read data indicating a quantity of solvent within the received solvent cartridge from an electronic data storage device associated with the received solvent cartridge, said data reader comprising a plurality of electrical contacts arranged to make contact with corresponding electrical contacts of the received solvent cartridge; and a controller arranged to generate update data usable to modify data stored on each of said electronic data storage devices (201, 301) and to modify data stored on said electronic data storage devices based upon said update data, such that data stored on each electronic data storage device indicates a respective updated quantity of fluid in said respective printing fluid cartridge.