Reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant (buffered or saturated) concentrations of each participants of the redox reaction.
Reference electrodes are used to build an electrochemical cell in conjunction with an electrode the potential of which is to be determined. Each electrode represents a half cell; both are required to complete the circuit and measure the unknown potential.
212 Calomel electrode (Porous ceramic junction)
232 Calomel electrode (Porous ceramic junction)
801(217) Double liquid-junction calomel electrode (Porous ceramic junction)
802 Calomel electrode (Porous ceramic junction)
RE-1A Mercuric oxide electrode (Porous ceramic junction)
RE-1C Ag/AgCl electrode (Porous ceramic junction)
RE-2A Double liquid-junction Ag/AgCl electrode (Porous ceramic junction)
RE-2B Calomel electrode (Porous ceramic junction)
RE-2C Hg/Hg2SO4 electrode (Porous ceramic junction)