An ink filling apparatus is constituted by an access unit for reading an amount of ink consumed in an ink cartridge which needs to be refilled from a storage unit provided on the relevant cartridge and a filling controlling unit for determining an amount of ink on the basis of the data. The signature circuit outputs the signature information through a transistor for adjusting impedance to reduce a chip size by omitting an additional logic circuit for the signature circuit. Positioned within the sealed, compressible container are first and second magnets that are separated by a first distance when a fluid within the sealed annular volume is at a first pressure.