There are two basic classes of anodes. Anodes that electro-chemically react to generate the electrical current flow includes magnesium, zinc and aluminum as well as graphite and high silicon cast iron impressed current anodes. These anodes consume at a defined rate based on the generated current. We can define their consumption rate in terms of kgs of mass consumed for every so many amp-years of operation. There is always a consideration for utilization of the anode. You can never fully consume 100% of the anode mass. At some point, the anode degradation impacts the anode's ability to perform. So, it is quite possible for these electro-chemically reactive anodes to calculate the expected anode life. The second class of anodes are electro-catalytic. They are not a reactant but promote electro-chemical reactions. These catalytic type anodes are either platinum based or MMO type. MMO is short for mixed metal oxide. MMO is a coating that consists of an iridium (or ruthenium) metal oxides and other components. Because these anodes are catalytic, they do not consume in the same manner as the electro-chemically reactive anodes. There is no measurable loss of mass with MMO anodes. This is because they are not directly reacting with the electrolyte. However, these catalytic anodes do have their own definable anode life also based on amp-years of operation.