What is the function of the reference electrode

The reference electrode provides a constant potential regardless of the composition of the solution it is placed in. The voltage difference between the reference and measuring electrodes is a function of the pH value of a solution. Common reference systems in use are Silver/Silver chloride/ (Ag/AgCl) and Mercury/Calomel (Hg2Cl2). The Silver/Silver Chloride reference is far the most frequently employed because it has universal applicability, a wide operating temperature range and is relatively non-toxic.